B.Sc. First Year�Semester-I�Paper Name:– Biodiversity of Chordates �Paper No.-II

SWAMI RAMANAND TIRTH MARATHWADA UNIVARSITY , NANDED

Gramin (ACS)Mahavidyalaya vasantnagar, Kotgyal Tq. Mukhed Dist. Nanded

Dr. S. K. Pawar

Head and professor

Department of Zoology

Syllabus

Subject:- Zoology, Semester:- I, Paper no. -II

Paper Name:- CCZ -I - Biodiversity of Chordates

UNIT – I

1. Introduction of Chordates, Salient features and classification of chordates up to class level.

Origin and Ancestry of Chordata.

2. Protochordata:-

Urochordata:- General features and Phylogeny of Urochordata;

Cephalochordate:- General features and Phylogeny of Cephalochordate.

3. Agnathia :- General characters and classification of Agnathia with suitable examples.

4. Cyclostomata:- General characters with suitable examples.

UNIT – II

1. Pisces:- General characters and classification up to order level with suitable examples;

Scoliodon (Dogfish):-

1. External morphology,

2. Digestive system,

3. Respiratory system,

4. Circulatory System,

5. Nervous system,

6. Urinogenital system.

7.Economic importance of Fishes.

2. Amphibia:- General characters and classification up to order level with suitable examples;

Parental care in Amphibians; Hibernation and aestivation in Frog.

UNIT – III

1. Reptiles:-

General characters and classification up to order level with suitable examples ; Poisonous and non-poisonous snakes; Biting mechanism in snakes; Importance of snake Venom.

2. Aves:-

General characters and classification up to order level with suitable examples ; Flight adaptations in birds; Migration in birds.

UNIT – IV

1. Mammals:-

General characters and classification up to order level with suitable examples.

1. Rat:-

1. External characters,

2. Digestive system,

3. Respiratory system,

4. Circulatory system,

5. Nervous system - Brain and spinal cord, Eye and Ear.

UNIT-I

Chordata = Cord bearing

Notochord =Back cord (Backbone)

Chordate Species 49,000

1.Urochordate and Cephalochordate – 2,500

2. Sub-Vertebrata - 46,500

3. Fishes -25,000

4. Amphibians - 25,00

5. Reptiles - 6,000

6. Birds - 9,000

7. Mammals - 4,500

Introduction of Chordates:-

Introduction of Chordates:-

Introduction of Chordates:-

• Chordates have three embryonic cell layers.
• They also have a segmented body with a coelom and bilateral symmetry.
• Chordates have a complete digestive system and a closed circulatory system.
• Their Nervous System is centralized.
• There are four additional traits that are unique to chordates.
• These four traits, shown in define the chordate phylum.
• The tail is opposite the head and extends past the anus.
• The nerve cord runs along the top, or dorsal, side of the animal.

• However, in many chordates, including humans, all four traits are present only during the embryonic stage.
• After that, some of the traits disappear or develop into other organs.
• For example, in humans, pharyngeal slits are present in embryos and later develop into the middle ear.

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• The notochord lies between the dorsal nerve cord and the digestive tract.
• It provides stiffness to counterbalance the pull of muscles.
• Pharyngeal slits are located in the pharynx.
• The pharynx is the tube that joins the mouth to the digestive and respiratory tracts.

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Primary diagnostic Characteristics of Chordata:-

Animals in the phylum Chordata share four key features that appear at some stage during their development.

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In chordates, four common features appear at some point during development:-

1. Notochord.
2. Dorsal hollow nerve cord.
3. Pharyngeal slits.
4. Post-anal tail.

1. Notochord:-

• The chordates are named for the notochord:- A flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
• It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
• In some chordates, the notochord acts as the primary axial support of the body throughout the animal’s lifetime.
• In vertebrates, the notochord is present during embryonic development, at which time it induces the development of the neural tube which serves as a support for the developing embryonic body.
• The notochord, however, is replaced by the vertebral column in most adult vertebrates.

2.Dorsal Hollow Nerve Cord:-

• The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development.
• In chordates, it is located dorsally to the notochord.
• In contrast to the chordates, other animal phyla are characterized by solid nerve cords that are located either ventrally or laterally.
• The nerve cord found in most chordate embryos develops into the brain and spinal cord, which comprise the central nervous system.

3. Pharyngeal Slits:-

• Pharyngeal slits are openings in the pharynx that extend to the outside environment.
• In organisms that live in aquatic environments, pharyngeal slits allow for the exit of water that enters the mouth during feeding.
• Some invertebrate chordates use the pharyngeal slits to filter food out of the water that enters the mouth.
• In vertebrate fishes, the pharyngeal slits develop into gill arches, the bony or cartilaginous gill supports.
• In most terrestrial animals, including mammals and birds, pharyngeal slits are present only during embryonic development.
• In these animals, the pharyngeal slits develop into the jaw and inner ear bones.

4. Post-anal Tail:-

• The post-anal tail is a posterior elongation of the body, extending beyond the anus.
• The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species.
• In some terrestrial vertebrates, the tail also helps with balance, courting, and signaling when danger is near.
• In humans and other apes, the post-anal tail is present during embryonic development, but is vestigial as an adult.

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Origin Of Chordates:-

Origin Of Chordates:-

Introduction:-

It proposes that the origin of chordates, which took place about 570 million years ago during the Precambrian, must be from some deuterostomes (animals in which the mouth is not formed from the blastopore of the early stages of development and that includes echinoderms, hemichordates and chordates).

• Here we shall discuss the origin of earlier chordate ancestors of the vertebrates.
• That chordates have originated from the invertebrates is not questioned by most zoologist now-a-days.
• Since the earlier chordate ancestors were soft-bodied forms, they left no fossil remains to us clues as to their origin.
• Therefore, only basis for finding out the origin of earlier chordates is available from the resemblance between the lower chordates and the invertebrates.
• There are some structural features shared by them, such as bilateral symmetry, antero-posterior body axis, triploblastic coelomate condition, metameric segmentation, etc., may be considered as basis of their common ancestry.

Ancestry of Chordates:-

Ancestry of Chordates:-

• Similarities existing between some invertebrates and the chordates have led to the enunciation of several theories on the origin of chordates.
• All these theories postulate that the chordates originated either directly from some invertebrates or through the intervention of some invertebrate chordates.
• Almost every invertebrate phylum—Coelenterata, Nemertean, Phoronid a, Annelida, Arthropoda and Echinodermata—has been suggested.
• But these theories are far from being satisfactory and convincing and have only a historical value.
• Only the echinoderm theory has received some attention and acceptance and shall be considered and evaluated under deuterostome line of chordate ancestry.

General characters of Cephalochordate:-

General Characters Of Cephalochordata:-

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• Body is fish-like and is useful for burrowing and swimming.
• It has a head.
• It shows a tail.
• Appendages are absent.
• Dorsal, caudal and ventral fins are present.
• Body-wall shows one- cell thick, non-ciliated epidermis, dermis, connective tissue, striated muscle and parietal peritoneum.
• It has no exoskeleton.
• Notochord extends from the anterior end to posterior end.
• Enterocoele coelom is present.
• However, reduced in the pharyngeal region by atrium.

• Alimentary canal is long.
• It includes a large pharynx with many gill-slits  ciliary mode of feeding is developed.
• Gills will perform respiration.
• Circulatory system is closed.
• Heart and respiratory pigments are absent.
• Hepatic portal system is present.
• Excretory system shows paired protonephridia with solenocytes.
• Brain is not present
• Two pairs of cerebral and several pairs of spinal nerves are present.
• Sexes are separate.
• Gonads are metameric ally arranged and with out conducts.
• Asexual reproduction will not take place.
• Fertilization is external.

General characters of Urochordata:-

General Characters Of Urochordata:-

• Their chordate features are clearly seen in the larval stages.
• All Urochordates are marine and occur in all the seas.
• Majority of them are sedentary and some are pelagic. 
• Body shows variation in size and form.
• The body is un segmented and has no tail.
• The body is covered by a test.
• It is formed by tunicate which is rallied to cellulose.
• Hence the name Tunicate.
• Body wall shows one-layered epidermis, dermis is made by connective tissue and muscles, and atrial empathy.
• Cleome is absent.

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• Atrial cavity surrounds the pharynx, into this cavity the gill slits anus and genital ducts will open.
• It opens through atrial aperture.
• Larva has notochord in the tail.
• It disappears during metamorphosis.
• Respiratory system contains gills in the pharyngeal wall.
• Ciliary mode of feeding is common.
• Open type of Circulatory system is seen.
• The heart is ventral and it periodically reverses its function.
• Nervous system is represented by a single dorsal ganglion in the adult.
• Excretion is carried on by nephrocytes.
• Asexual reproduction is by budding.
• Bisexual animal and cross fertilization is favored.
• Fertilization is external.
• Development includes a minute, free swimming tadpole larva with a tail, a dorsal nerve cord, and a notochord in the tail.

General characters of Agnatha:-

General characters of Agnatha:-

• Jaws are absent.
• Paired fins are generally absent.
• Early species had heavy bony scales and plates in their skin, but these are not present in living species.
• In most cases the skeleton is cartilaginous.
• The embryonic notochord persists in the adult.
• Seven or more paired gill pouches are present.

• Slander, eel-shaped body.
• 7 external gill openings.
• The notochord persists in the adult.
• Skeleton is composed of cartilage.
• There are no paired fins.

• They have a light sensitive pineal eye.
• A pineal eye is a third eye.
• Fertilization of eggs takes place outside the body.
• No scales, smooth, slimy skin to escape predators.

General character of Cyclostomes:-

General Characteristics of Cyclostomes:-

• The body is round and elongated like an eel.
• The paired fins are absent.
• Median fins with cartilaginous fin rays.
• No paired appendages.
• The skin is soft and smooth, devoid of any scales.
• Spleen is absent.
• The exoskeleton is absent.
• The endoskeleton is cartilaginous with no bones.
• The notochord is present throughout their lives.

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• The digestive system is devoid of any stomach.
• The nostril is single and median.
• The gills are five to sixteen in pairs.
• The heart is two-chambered.
• The brain is visible.
• The lateral line acts as a sense organ.
• About ten pairs of cranial nerves are present.
• The sexes are separate.
• Some hagfish species are believed to be hermaphrodite.
• A pair of mesonephric kidneys make up the excretory system.
• Development may be direct or indirect.
• E.g., Petromyzon and Maxine.

UNIT-II

Different types of fresh or marine water Fishes:-

General characters of Pisces:-

General Characteristics of Pisces:-

• They are found in fresh, marine, and brackish water.
• The body is usually streamlined.
• Some have a spindle-shaped or elongated body as well.
• Their body is distributed into a head, trunk and tail.
• They swim with the help of their tail.
• Paired and unpaired fins represent the appendages.
• These help the fish to balance while swimming.
• The lateral line system functions as a sensory organ to sense the disturbances in the near by environment.
• The body is covered with thick-seated scales, which helps by providing protection to the internal organelles.

• The gills help in respiration.
• Closed type blood circulation is observed.
• The internal skeleton is bony or cartilaginous.
• These are cold-blooded organisms.
• They may be herbivores or carnivores, oviparous or ovoviviparous.
• The sexes are separate.
• Fertilization may be external or internal.
• They lack extra-embryonic membranes.
• The digestive system is well-developed.
• The nervous system comprises of the brain and ten pairs of the cranial nerves.

External Morphology of Scoliodon:-

1. Shape, Size and Colour:-

2. Sexual Dimorphism:-

3. Division of Body:-

4. Head:-

5. Trunk:-

6. Tail:-

7. Fins:-

8. Median Fins:-

9. Lateral Fins:-

10. Skeletal Structures :-

Shape, Size and Colour:-

• Scoliodon is commonly known as Dogfish.
• It has a long, laterally compressed spindle-shaped body tapering at both ends.
• The body colour is dark grey above and pale white beneath, while the portions of the caudal fin are more or less dark.
• The adult specimen measures from 30 to 60 cm in length.
• Body covered with placoid scales which are backwardly directed spines and are embedded in the dermis.
• The body surface is rough.

Sexual Dimorphism:-

• Male specimen bear a pair of rod-shaped copulatory organs at the inner margins of the pelvic fins called claspers.
• Claspers are the modified parts of pelvic fins.
• Claspers are stiff rod-like appendages having a groove on its dorsal surface which leads into a cavity.
• The siphon arises at the base of the clasper.

Division of Body:-

• The body is divisible into head, trunk and tail, though there are no distinct boundaries between these regions.

Head:-

• The head is strongly compressed, dorsa-ventrally and is produced in front into a wedge-shaped snout.

Trunk:-

• The trunk is almost elliptical in transverse section.
• Its thickest part lying in front of the middle of the body.
• It is gradually tapers behind into the tail.

Tail:-

• The tail is laterally compressed and is bent upwards at a small angle and fringed with a caudal fin.
• This kind of tail is known as heterocercal tail.

Fins:-

• Provided with two sets of fins which are flattened expansions of the skin supported by cartilaginous rods and horny fin rays- These are unpaired or median fins and paired lateral fins.

Median Fins:-

• i) Scoliodon have two sets of median fins situated along the central line of the body a ventral or anal fin and a caudal fin, which is the tail, and an anal fin located at the underside behind the anus.
• ii) The first dorsal fin is large and triangular in shape and has a basal lobe.
• iii) The second dorsal fin is also triangular but is very small and is situated midway between the first dorsal and the tip of the tail.
• iv) The caudal fin extends along the dorsal and ventral surfaces of the tail in the median line and forms a dorsal and ventral lobe.

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v) The dorsal lobe is very much reduced and forms only a low ridge along the greater part of the upper surface but the ventral lobe is well developed and is divided into two parts, the anterior part being much larger and more extensive than the posterior.

vi) The ventral or anal fin is situated in the mid-ventral line just in front of the caudal fin, and opposite the second dorsal.

II) Lateral Fins:-

• The lateral fins are paired pectoral and pelvic fins.
• The large pectoral fins originate from the ventro-lateral margins of the body and immediately behind the gill-clefts.
• The pelvic fins are much smaller than the pectoral fins which arise close together from the ventral surface at the junction of the trunk and tail.
• In Male the medial part of pelvic fins is produced into a dorsally grooved, stiff rod like clasper used for copulation.
• All fins are directed backwards a feature that support in forward progression.

Skeletal Structures :-

• Scoliodon has well-developed exoskeletal and endoskeleton structures.
• The exoskeleton includes predominantly the scales which are present all over the body.
• The endoskeleton embraces the axial and appendicular skeleton.

Placoid Scales:-

• It consist of two parts a wide rhomboidal basal plate and a flat trident spine arising from its center.
• The spine projecting out of the skin is backwardly directed and formed by one median and two lateral spines.
• Placoid scales are rough to the Placoid Scales

A. Dorsal view

B. Ventral view

Eyes:-

• On each lateral side of head a large circular eye is present.
• The pupils are narrow and vertical.
• Eyes have paired poorly-formed immovable eye-lids, nictitating membrane located antero-ventrally.

Digestive System of Scoliodon:-

• The digestive system of Scoliodon includes:-
• Alimentary canal:-
• Mouth
• Buccal cavity
• Pharynx
• Oesophagus
• Stomach
• Intestine
• Rectum
• Cloaca
• Digestive gland:-

1. Liver

2. Pancreas

3. Rectal gland

4. Spleen

Alimentary canal:-

1. Mouth:- It is semi-oval slit bounded by upper and lower lips.

2. Buccal cavity:-

• Mouth leads right into a dorso-ventrally flattened buccal cavity lined by jaws.
• Teeth are homodont ,sharply pointed and directed backwards.
• They are polyphyodonty and arranged in many rows.
• Teeth help in grasping the prey.
• On the floor of the buccal cavity thick, flat, and non-muscular tongue is present.

3. Pharynx:-

• Posteriorly buccal cavity opens into pharynx .
• Lateral side of pharynx contains an oval pit of spiracle and five separate gill-slits

4. Oesophagus:-

• Pharyngeal space cavity narrows down posteriorly into a short tube, the Oesophagus.

5. Stomach:-

• Stomach is a U-shaped large cavity.
• Its proximal limb, the cardiac stomach is longer, wider and distensible.
• Its distal limb is shorter and narrow and is known as pyloric stomach.
• At the junction of cardiac and pyloric stomach a small blind sac in addition to a sphincter valve is present.
• Pyloric stomach ends with a strong circular muscle band known as pyloric valve guarding its opening into a thick-walled muscular chamber, the bursa antenna

6. Intestine :-

• Bursa antenna is followed by intestine.
• It is a straight wide tube.
• Its narrow anterior part gets the bile and secretions of pancreatic ducts.
• In Scoliodon, the intestine becomes folded anticlockwise into a scroll valve or spiral valve.
• It gives increased surface area for absorption.
• The last part of gut is referred to as rectum.
• It is a short and narrow tube opening behind through anus into the ventral cloaca.
• A small finger-like rectal gland of unknown function opens dorsally into the rectum .

7. Rectum:-

• The rectum opens into the cloaca.
• A tubular rectal gland opens into the rectum.

8. Cloacal Opening:-

• this is the last opening of digestive system called as Cloacal aperture.
• It is a common opening for rectal glad and rectum.

• Digestive glands:-

1. Liver:-

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2. Pancreas:-

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3. Rectal gland:-

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4. Spleen:-

• Digestive glands:-

1. Liver :-

• It is a big yellowish bilobed gland.
• Bile is collected in V-shaped gall bladder, lies inside the right lobe of liver.
• A narrow bile duct leaves the gall bladder and opens into the anterior end of the intestine.
• Bile duct also gets branches from the lobes of liver.
• It secretes bile, stores glycogen and fat and destroys worn out erythrocytes of blood.

2. Pancreas:-

• It is a compact whitish or pale bilobed gland running parallel to the posterior part of cardiac stomach and a smaller ventral lobe closely applied to the pyloric stomach.
• The small pancreatic duct open into the intestine just opposite the opening of the bile duct .

3. Rectal gland:-

• Rectal gland is a small finger like body attached by its duct to the dorsal side of rectum into which it opens.
• It is highly vascular and composed of lymphoid tissue.
• Its function is unknown.

4. Spleen:-

• It is a large gland closely attached to the cardiac and pyloric stomach.
• It has no physiological relation with alimentary canal and functionally associated with circulatory system.

Food and physiology of digestion:-

• Scoliodon is a predaceous carnivore feeding mainly on other fishes.
• Its diet can also consist of crabs, lobsters and worms.
• Food as a whole is swallowed; no digestion takes place in buccal cavity.
• Main digestion occurs inside the stomach via the movement of Pepsin and HCI of gastric juice.
• Bile and pancreatic juice containing trypsinogen, amylopsin and lipase act upon the semi-digested food in the gut.
• Scroll valve in intestine serves to retard the speed of passage of food to amplify the time of digestion and increase the surface of absorption .

• In Scoliodon the respiration is aquatic, since the animal resides in water.
• It breathes by means of gills borne in a series of gill-pouches on either lateral side of the pharynx.
• Water enters the mouth and after passing through the buccal cavity, pharynx, gill- pouches bearing gill-lamellae, goes out through the external gill-slits after bathing the gills.

Respiratory system of Scoliodon:-

Respiratory Organs:-

• There are five pairs of gill- pouches bearing gills, arranged in a series behind the hyoid arch in the lateral walls of the pharynx.
• Each gill-pouch is compressed antero-posteriorly and communicates with the cavity of the pharynx through a large internal branchial aperture and with the exterior through a narrow external branchial aperture.
• The endodermal mucous membrane of gill-pouches or intrabronchial septa is raised into a series of horizontal folds to form lamelliform branchial lamellae or gill-filaments.

• The branchial lamellae have a rich blood supply, and they have a very thin covering membrane through which blood is exposed to sea water for an exchange of gases.
• Each gill-pouch has two sets of gill-lamellae, one on its anterior wall and the other on the posterior.

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• Each set of lamellae is a half gill or hemibranch, so that gill-pouch has two hemibranchs.
• The gill-pouches are separated from each other by fibro-muscular partition called the inter-branchial septa.
• The intrabronchial septa extend well beyond the branchial lamellae, then each bends posteriorly to form a flap which protect the lamellae as well as external gill-slit.
• he inner part of each intrabronchial septum has a supporting cartilaginous visceral arch with slender gill-rays.
• Visceral arches also give out rigid comb-like gill-rankers which project inwards to protect the internal branchial apertures from entering the food.

• Each visceral arch supports the posterior branchial lamellae or hemibranch of posterior gill-pouch and the anterior branchial lamellae of the anterior gill-cleft.
• These two hemibranchs or hemibranchs with their intrabronchial septum and the visceral arch constitute a complete gill or holobranch.

• The posterior hemibranch of a septum has longer lamellae than the anterior one.
• Thus, a gill-pouch has two hemibranchs belonging to two adjacent gills.
• In Dogfish (Scoliodon), the hyoid arch bears only a hemibranch on its posterior surface, the first four branchial arches has holobranchs and the fifth branchial arch is without any gill (a branch).
• Thus, it has nine hemibranchs.

• Between the mandibular and hyoid arches or the first internal gill-slit on either lateral side of pharynx is a spiracle.
• In most elasmobranchs the spiracle bears minute branchial lamellae forming a false gill and opens to the exterior by an external branchial aperture.
• It is supplied with arterial blood and plays no part in respiration.
• But in Dogfish (Scoliodon) the spiracles are vestigial pits in the pharynx with no lamellae and external branchial apertures.

Mechanism of Respiration:-

1. Inspiration:-

• The floor of the buccopharyngeal cavity is depressed by the contraction of hypobranchial (hypoglossal) muscles due to which the visceral arches expand the wall of the pharynx, so that sea-water containing dissolved oxygen rushes in through the opened mouth.
• Entry of water into external branchial apertures is prevented by an anterior fold of skin on each gill-pouch.

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Expiration:-

• During expiration the mouth becomes closed by the action of adductor muscle.
• Now the buccopharyngeal floor is raised, and contractions of the wall of the pharynx force the water into internal branchial apertures, the Oesophagus being closed, and then into gill-clefts, where it washes the branchial lamellae and goes out of the external branchial apertures.
• The respiratory movements are caused by pharyngeal muscles which are innervated by V, VII, IX and X cranial nerves and the hypoglossal spinal nerve.

Physiology of Respiration:-

• In the branchial lamellae the blood flows from the tip towards the base, that is in a direction opposite to that of the water current, so that the blood just before leaving the lamellae meets the highest concentration of oxygen and the lowest of carbon dioxide, thus, an efficient exchange of oxygen and carbon dioxide takes place between the blood and sea-water.

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• Fresh sea-water entering the gill- pouches with the respiratory current contains oxygen dissolved in it.
• This water is separated from the blood contained within the capillaries of the gill-lamellae merely by the thin and permeable membranous walls of the capillaries.
• The oxygen of the water passes by endosmosis through the thin capillary walls into the blood, and at the same time the carbon dioxide of the blood passes into the water by a process of exosmosis.
• The oxygen is conveyed by the blood to all the parts of the body, while carbon dioxide brought to the gills in the venous blood is eliminated by the water of the outgoing respiratory current.
• As the blood makes a complete circuit in the capillaries of the gills in a very short time, it is evident that exchange of gases also takes place very quickly.

1. Circulatory System of Scoliodon:-

The circulatory system consists of:-

• The circulatory fluid, called blood,
• The heart,
• The arteries and
• The veins.

Blood:-

• The blood consists of a colourless plasma and corpuscles are suspended in the plasma.
• Two kinds of corpuscles are encountered; the RBC (or erythrocytes) and the WBC (or leucocytes).
• The erythrocytes are oval bodies containing a nucleus.
• The hemoglobin is present in the erythrocytes.
• The leucocytes are amoeboid in structure.

Heart:-

• The heart is a bent muscular tube and consists of the receiving parts, comprising of a sinus venosus and a dorsally placed auricle, and the forwarding parts, consisting of a ventricle and a conus arteriosus.
• The heart is situated on the ventral side of the body between two series of gill-pouches.

Receiving parts of the heart:-

• The sinus venosus is a thin-walled tubular chamber.
• The sinus venosus is highly contractile and the beating of the heart originates from this part of the heart.
• Two great veins, the ductus Cuvier, open into the sinus venosus, one on each lateral side.
• Two hepatic sinuses enter the sinus venosus posteriorly.
• The sinus venosus opens into the auricle by sin auricular aperture which is guarded by a pair of valves.
• The auricle is a large, triangular and thin walled chamber situated dorsal to the ventricle but in front of the sinus venosus.
• The auricle communicates with the ventricle through a slit-like auriculoventricular aperture guarded by two lipped valves.
• The receiving chambers, (sinus venosus and auricle) receive the venous blood from all parts of the body.

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Forwarding parts of the Heart:-

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The ventricle:-

• This has a very thick muscular wall and the inner surface gives many muscular strands making its spongy texture.
• It is an oval chamber and constitutes the most prominent part of the heart.

The conus arteriosus:-

• It is a stout median muscular tube arising from the ventricle.
• The lumen of the conus arteriosus is provided with two transverse rows of semi-lunar valves.
• To keep the valves in position the free ends of the valves are attached to the ventricular wall by chordae tendinea.
• The conus arteriosus is continued forward as the ventral aorta.

Working of heart:-

• The main function of the heart is to receive the deoxygenated blood from all parts of the body and to pump it for aeration to the gills.
• Such a type of the heart is designated as the venous or branchial heart.
• The blood also flows through the heart only once (single circulation).
• For this purpose, the different chambers of the heart rhythmically contract at regular intervals in a definite sequence—first sinus venosus → auricle → ventricle → conus arteriosus.
• Contraction of the heart is called systole and relaxation is called diastole.
• The valves at different places prevent the Heart of Scoliodon Ventral view Diagrammatic L.S. of Heart 6 backward flow of blood into the preceding chambers.
• The heart walls are supplied oxygenated blood through coronary vessels.

Arterial System of Scoliodon:-

The arterial system of Scoliodon is divided into two distinct categories of arteries.

These are:-

A. The afferent branchial arteries arising from the ventral aorta which bring the deoxygenated blood to gills for oxygenation and

B. The efferent branchial arteries which originate from gills and convey the oxygenated blood to the different parts of the body.

Afferent branchial arteries:-

• The ventral aorta is situated on the ventral surface of the pharynx and extends up to the posterior border or the hyoid arch.
• The ventral aorta divides into two branches called innominate arteries, which again bifurcates into the first and second afferent branchial arteries.
• The third, fourth and fifth afferent arteries arise from the ventral aorta.
• Each afferent branchial artery arises from the ventral aorta by independent opening except the anterior most pairs which arise by a common opening.

Efferent branchial arteries:-

• The afferent branchial arteries break up into capillaries in the gills.
• From the gills the blood is collected by efferent branchial arteries.
• There are nine pairs of efferent branchial arteries and these are equally distributed on each side.
• The first eight arteries form a series of four complete loops around the first four gill-slits and the ninth efferent branchial artery collects blood from the demi branch of the fifth gill- pouch and from where blood is poured into the fourth loop.
• In addition to short longitudinal connectives connecting the four loops, these are further connected with each other by a network of longitudinal commissural vessels called the lateral hypobranchial chain.

• From each efferent branchial loop arises an epibranchial artery.
• The four pairs of epi- branchial join in the mid-dorsal line to form the dorsal aorta.
• The ninth efferent branchial artery has no epibranchial branch but joins with the eighth efferent branchial artery.

Anterior arteries:-

• The head region gets the blood supply from the first efferent branchial artery and partly from the proximal end of the dorsal aorta.

Arteries from the first efferent branchial (hyoidean efferent) are:-

(a) The external carotid,

(b) The afferent spiracular and

(c) The hyoidean epibranchial which in turn receives a branch from dorsal aorta.

• The external carotid artery originates from the first collect or loop and divides into a ventral mandibular artery giving branches to the muscles of the lower jaw and a superficial hyoid artery which supplies the second ventral constrictor muscle, the skin and the subcutaneous tissue beneath the hyoid arch.
• The afferent spiracular artery after originating from the middle of the hyoidean efferent, proceeds forward as the spiracular epibranchial artery and enters the cranial cavity.
• Just before its entry into the cranial cavity it sends a great ophthalmic artery to the eye ball.
• Immediately after the entry to the cranium it joins with a branch from the internal carotid to form the cerebral artery.
• The cerebral artery immediately divides into an anterior and a posterior cerebral artery which supply the brain.
• The hyoidean epibranchial artery runs forwards and inwards to the posterior border of the orbit and gets an anterior branch from the dorsal aorta.

It divides immediately into:-

• (a) the stapedial artery which gives off the inferior orbital artery and runs forward as the superior orbital artery supplying the six eye muscles and the superficial tissue above the auditory capsule.
• The superior orbital artery gives a large buccal artery which runs as the maxillofacial artery.
• The maxillofacial gives several arteries to the muscles of the upper jaw, the olfactory sac and the rostrum,
• (b) the internal carotid artery passes inward and enters the cranium where it bifurcates into two branches
• One of the branches unites with its fellow from the opposite side and other branch unites with the stapedial.

Dorsal aorta and its branches:

• The dorsal aorta is formed by the union of epibranchial arteries.
• It runs posteriorly and is situated ventral to the vertebral column.
• It is continued up to the tip of the tail as the caudal artery.

Along the anteroposterior direction the following arteries have their origin from the dorsal aorta:

(a) Several buccal and vertebral arteries are given off anteriorly.

(b) A pair of small subclavian arteries arise from near the origin of the fourth epibranchial arteries.

The subclavian artery gets the eicosanoid artery on its way and divides into:

(i) A branchial artery to the pectoral girdle and pectoral fin,

(ii) An anterolateral artery to the body musculature and

(iii) A dorsolateral artery to the dorsal musculature.

(c) A large coeliac mesenteric artery arises just behind the origin of fourth epibranchial artery.

• It divides into a smaller coeliac artery and a larger anterior mesenteric artery.

(d) A lien gastric artery originates posterior to the coeliac mesenteric artery and gives off

(i) An ovarian (in females) or spermatic artery (in males) to gonad,

(ii) A posterior intestinal artery to the posterior part of the intestine,

(iii) A posterior gastric to the posterior part of the cardiac stomach and

(iv) A splenic artery to the spleen.

(e) Series of paired parietal arteries emerge out behind the subclavian artery.

• Each parietal gives a dorsal parietal artery and a ventral parietal artery.
• The dorsal parietal artery supplies the dorsolateral musculature, the vertebral column, the spinal cord and the dorsal fin.
• The ventral parietal artery supplies the ventral muscles and the peritoneum.
• The ventral parietal gives renal branches to the kidneys.

(f) A pair of iliac arteries extend to the pelvic fin as femoral arteries.

Hypobranchial chain:-

• A lateral hypobranchial chain is formed by a network of slender arteries arising from the ventral ends of the loop of the efferent branchial arteries.
• Four commissural vessels arise from the lateral hypobranchial chain which on the ventral wall of the ventral aorta unites to form a pair of median hypobranchial which communicate with one another by transverse vessels.
• Posteriorly the median hypo-branchial unite to form a median coracoid artery which gives rise to the coronary artery and a pericardial artery.
• The pericardial artery gives off the common eicosanoid artery which in turn divides into left and right eicosanoid arteries each joining one subclavian artery.

Venous System of Scoliodon:-

• The deoxygenated blood from the different parts of the body is returned to the heart by veins which form irregular blood sinuses throughout their courses.
• The existence of extensive blood sinuses is a characteristic feature of the venous system of Scoliodon.

• The blood from entire body is returned to the heart by the veins.
• These veins are in different structure forming arteries which possesses valves which thin and prevent back flow of blood.
• Many veins are wide irregular spaces without definite walls called sinuses.

The venous system can be divided into the different systems viz.:-

1. Anterior cardinal system.
2. Posterior cardinal system.
3. Hepatic portal system and
4. Cutaneous system.

1. Anterior Cardinal System:-

• It collects blood from the anterior part of body especially head it consists of a pair of large vessels.
• Each jugular comprises olfactory, orbital, postorbital and the anterior cardinal sinuses.
• The olfactory sinus receives blood from the rostral region by facial vein.
• It opens into the ductus Cuvier and receives a hyoidean sinus from inferior jugular sinus.
• It also receives blood from the dorsal nutrient branchial sinuses of gills.
• A pair of inferior jugular sinus.
• These are small and median, one on either side which collect blood from the buccopharyngeal region, gill-pouches and heart and then open laterally into the ductus Cuvier.

2. Posterior Cardinal System:-

• This system collects blood from posterior part of the body which consists of a median caudal vein, two renal veins and two large posterior cardinal sinuses.
• The caudal vein runs at below the caudal artery and Hemal arch of the caudal vertebrae.
• It receives numerous branches on either side from the tail.
• The caudal artery bifurcates into right and left renal portal veins,
• the renal portal veins continue to the dorso-lateral margins of kidney and give out many afferent renal veins.
• It breaks up into capillaries in the kidney.
• The blood from the kidneys is collected by the efferent renal veins which join together and form a single vessel.
• In the region of oesophagus, the posterior cardinals expand into sacs and receive an oesophageal vein from oesphagus.
• Each posterior cardinal opens into the Cuvierian duct.

3. Hepatic Portal System:-

• The blood of alimentary canal and associated glands is collected by a number of veins called the hepatic portal vein.
• The hepatic portal vein is Venous System in Scoliodon-Ventral view 9 formed by the union of the anterior and posterior intestinal veins.

• The blood brought to the liver is distributed by fine capillaries and is collected by a second set of capillaries form two large thin-walled sinuses, the hepatic sinuses open into the sinus venosus by two small apertures.

4. Lateral Abdominal Veins:-

• The lateral abdominal veins collect blood from body wall, cloacal part and paired fins.
• In the posterior part both are connected by a commissural vein and receive an iliac vein from the pelvic fin.
• Anteriorly each vein receives a subclavian from pectoral fin and empties into the ductus Cuvier us.
• Lateral vein instead of joining with the sub-clavi an and opens separately into the pre-cavil.

5. Cutaneous System:-

• It includes mid-dorsal, mid-ventral and two lateral cutaneous veins.
• The cutaneous vein runs beneath the skin along mid-dorsal line and collects blood.
• The ventral cutaneous vein runs along the mid-ventral line beneath the skin and joins to lateral abdominal front to the cloacal vein.
• The lateral cutaneous vein runs along each side of lateral line and each empties its blood into the branchial vein.

Blood:-

• The blood of Scoliodon consists of colourless plasma and corpuscles RBCs (erythrocytes) WBCs (leucocytes).

Nervous system of Scoliodon:-

Nervous System of Scoliodon:-

The nervous system of Scoliodon divided into three parts

I. Central Nervous system:-

It includes brain and spinal cord.

II. Peripheral nervous system:-

It includes cranial and spinal nerves.

III. Automatic nervous system:-

I. Central Nervous system:-It includes

a) Brain and

b) spinal cord.

A) Brain:-

The brain is highly organized and shows much advancement.

It is divided into three parts

i) The forebrain,

ii) The midbrain and

iii) The hindbrain

1. The forebrain:-

• It consists of a massive undivided cerebral hemisphere.
• From the anterior end of cerebral hemisphere arise two stout olfactory peduncles.
• At each terminates of peduncle a large bilobed olfactory lobe.
• The olfactory lobes lie close to the olfactory sac.
• Each olfactory nerve is composed of many bundles of nerve fibers.
• The surface of the cerebrum is smooth and a neuropore-a small opening is present at the mid-ventral part.
• The posterior part of forebrain is diencephalon which is very short.
• The roof of Brain of Scoliodon
• Dorsal View,
• Ventral view,
• Diagrammatic section of the ventricle 10 diencephalon is thin, non-nervous and contains anterior choroid plexus.
• The lateral walls of the diencephalon form two thickened bodies called thalami.
• The infundibulum is dilated and form two oval thick-walled bodies called lobe inferiors.
• The lobe inferiors are the centers for gestation and smell.
• The hypophysis is attached to the infundibulum.
• The optic chiasma lies in front of infundibulum and is formed by the decussation of the nerve fibers of two optic nerves.

2. The midbrain:-

• It is large and consists of two round optic lobes.
• The optic lobes are situated behind the diencephalon.
• The floors of lobe and side walls are thicker.
• The midbrain is considered as the center of coordination.

3. The hindbrain:-

• It consists of a highly developed cerebellum and a medulla oblongata.
• The hind- brain controls swimming movements.
• The cerebellum is the center of coordination and contains a small cavity.
• The cerebellum divided into three lobes and well marked by two transverse furrows.
• The dorsal surface produces many irregular convolutions.
• The medulla oblongata is triangular, it controls respiration.
• It is connected by the transverse nerve band.
• The medulla oblongata roof is non-nervous and bears the posterior choroid plexus.
• The cerebral hemispheres contain narrow lateral ventricle.
• The ventricles of the brain are moderately developed.
• The third ventricle is extended to the cerebral hemispheres.
• The floor of the fourth ventricle is very much thickened, larger and extended dorsally into the cerebellum and is continuous behind with the cavity of the spinal cord.

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B. Spinal cord:-

• It shows definite advancement towards the plan of higher vertebrates.
• The grey matter is arranged into the dorsal and ventral horns and dorsal horns are united to form a single broad region.

II. Peripheral nervous system:-

• It includes the cranial nerves and spinal nerves.

a). Cranial nerves:-

There are 10 pairs of cranial nerves recognized by their serial Roman numbers as well as the names.

0). Nerve “0” Terminal or Pre-olfactory:-

• These are olfactory nerves originate from the olfactory lobes and innervate the olfactory sacs.
• These nerves are supply to the nasal septum and external nostril.

i). Nerve I Olfactory:-

• These are sensory, serves for smelling. Arise from olfactory lobe supply to olfactory sac.

ii). Nerve II Optic:-

• These are nerves are the optic nerves origin from the optic thalami, form the optic chiasma and supply the eyes.
• These are sensory in relation to light.

iii). Nerve III Oculomotor:-

• These are motor, controlling movements of eyeball, iris and lens.
• They arise from ventral surface of midbrain.
• They divided into four branches to innervate the inferior, superior and anterior recti muscles and the inferior oblique muscles of eye.

v). Nerve IV Trochlear or Pathetic:-

• These are motor, help in rotation of eye ball.
• They arise dorso-lateral surface of midbrain and supply the superior oblique muscle of eye.

v). Nerve V Trigeminal:-

• They are mixed nerves arise from antero-lateral sides of medulla.
• It bear a gasser Ian ganglion while still in the cranium and divide into 4 main branches
• Ophthalmic us superficial which supplies to the skin of the snout.
• The maxillaries which 11 is divided into maxillaries superior supplying nerves to the skin of upper jaw and maxillaries inferior innervating the posterior part of upper jaw

• The mandibular is innervate the muscles of the lower jaw.
• Another nerve is called as a)Ophthalmic us superficialis- sensory, supplies to the skin of snout, b) Ophthalmic us profundo's-is a sensory supply to the dorsal skin is snout c) Maxillaries- it divides into two branches. Maxillaries superior, supplies to the ventral skin of the snout. While maxillaries inferior supplies the skin of posterior part of upper jaw, and d) Mandibular- is a mixed nerve and supplies to the muscles of lower jaw, tongue and gill region.

vi). Nerve VI Abducens:

• The sixth cranial nerve is the abducens which supplies the posterior rectus muscle of the eye ball.

vii). Nerve VII Facial:

• The seventh is known as facial which divides into two branches
• 1) The Ophthalmic us superficialis.
• 2) A bundle of mixed nerves which subdivides into three
• a) Ramus buccal is innervating the canal of the snout,
• b) Ramus hyomandibular is supplying nerves to the lower jaw and throat, and
• c) Ramus palatines supply to the roof of the buccal cavity and the pharynx.

viii).Nerve VIII Auditory:

• It is sensory and helps in audition called auditory.
• It passes in auditory capsule and innervate the membranous labyrinth.

ix). Nerve IX Glosson-pharyngeal:

• It is a mixed nerve and divides into three branches.
• These nerves supplies branches to pharynx, pharyngeal muscles and mucous membrane surrounding to the first gill slit.
• i) Plerematic nerve runs along the anterior border of first gill pouch and
• ii) the post trimitic runs along its posterior border while iii) pharyngeal to mucous membrane of the pharynx.

x). Nerve X Vague or pneumogastric:

• It is the vague which arises by multiple roots and gives off many branches.
• The brachial nerves supplying the gills,
• the lateralis supplying the lateral line sense organs and gives numerous branches along its course iii) the visceral is supply visceral organs and heart

b) Spinal nerves:

• It arises from the spinal cord and has dorsal and ventral root.
• The dorsal root bears a ganglionic swelling and in an emerging out through the vertebral column.
• Cranial nerves in Scoliodon 12 These roots unite and form a common mixed nerve. Each spinal nerve gives three branches

a) Ramus dorsalis,

b) Ramus ventral is, and

c) Ramus communicans.

III. Autonomous nervous system:

• This system is made up of a series of paired ganglia irregularly arranged on the dorsal wall of the kidney and the posterior cardinal sinuses.
• The largest ganglions are gastric ganglion which sends nerves to the viscera.

Sense Organs of receptor organs:-

The nervous system is associated with highly developed sense organs which include the paired olfactory, optic or photoreceptor, Stator- acoustic organs, the lateral line organs or neuromasts and the Ampullae of Lorenzen.

1. Olfactory organs:-

• There are two blind sac-like olfactory organs situated in front of the mouth.
• Olfactory sacs are located in a cartilaginous capsule and the mucous membrane is thrown into two series of folds called Schneiderian folds which are placed by the median raphe.
• The Schneiderian folds are composed of olfactory sense cells and supporting cells.
• Physiologically nasal opening is divided by three muscular valves into a median ex-current siphon and a lateral incurrent siphon.

Eyes or photoreceptor Organs:-

• Scoliodon has a pair of large and well developed eyes or photoreceptors, housed in orbits of the cranium.
• Eyes are large but separated by a sufficient distance so that binocular vision is not possible. Because of non-contractile pupil and little change in lens shape power of accommodation is poor.
• On the other hand, lens can be shifted forward and catch more light.
• Due to the presence of tapetum of guanin plates Scoliodon can achieve maximum light stimulation in dim conditions and prevent light scattering (blurring or halation) in bright condition.
• Normally Scoliodon are long sighted and colour blind because the absence of cones in retina.

Stator-acoustic Organs (Internal Ears or membranous labyrinths):-

Stator-acoustic Organs (Internal Ears or membranous labyrinths):-

• The internal ear of each side is a closed ectodermal sac, the membranous labyrinth which is enclosed within the cartilaginous auditory capsule one on either poster-lateral side of cranium.
• It consists of two parts-the central otosaccus and three peripheral semicircular canals.
• The otosaccus is laterally compressed and differentiated into a dorsal and anterior part.
• The utriculus, a ventral and posterior part the sacculus.
• Olfactory organs in Scoliodon Eye Mussel and their nerve supply 13 The sacculus is called lagena cochleae is the posterior outgrowth while anterior outgrowth is called recesses utriculi.
• The three slender semicircular canals arise from otosaccus and open into it.
• At the top of utriculus arise anterior vertical and horizontal semicircular canals and form independent ampullae before opening into the middle of the utriculus.
• The posterior vertical canal which arises from sacculus form complete circle and open ampulla into the lagena cochleae.
• The semicircular canals are arranged at right angles to one another. The cavity of sacculus communicates to the exterior by a long slender tube.
• The ductus endolymphatic us runs upward and pierces the roof of the cranium to open by a minute pore of the commissural occipital canal.
• The interior of membranous labyrinth, including the semicircular canals filled with a fluid the endolymph which is sea water.
• The endolymph contains the calcareous particles the otoliths.

• The space between the membranous labyrinth and the wall of the auditory capsule is the peri lymphatic space filled with a perilymph -the cerebra-spinal fluid.
• The peri lymphatic space opens to exterior by aperture and the fenestra lying immediately behind the opening of ductus endolymphatic us.
• The internal ear is not concerned with hearing but it maintains muscle-tone and detects acceleration of speed, change of direction and orientation.
• It concerned with balance or equilibrium with regard to gravity.
• Movements of endolymph and otoliths stimulate sensory nerve and ampullae, which inform the position in water.
• It also detects low frequency vibrations of water. Sacculus and lagena probably receive auditory stimuli.

Urinogenital System of Scoliodon:-

• The excretory organ consists of a pair of elongated kidneys.
• The kidney is non-functional at anterior portion but the posterior portion is greatly developed.
• The kidneys are nothing but coiled glandular uriniferous tubules.
• Every tubule consists of a Bowman’s capsule which encloses glomerulus and much coiled renal tubule.
• A few renal tubules open into a common collecting tubule.
• The tubules of kidney have extreme property of reabsorbing urea.
• The anterior non-renal portion of the kidney opens in to Wolffian duct while posterior tubules open into the ureters and into the urinogenital sinus.
• The mesonephric duct divides into two, the dorsal one is Wolffian duct and the ventral one is Mullerian duct.
• The Wolffian duct is nothing but the vas deferens in male and connected to the vasa efferent from the testis.
• The Mullerian duct is nothing but the oviduct in females.
• The pair of kidney is extremely elongated and extending from the root of liver to the cloacal region.

Male urogenital system of Scoliodon:-

Male reproductive system:-

• The testes are paired elongated organs.
• Testes are attached to the dorsal body wall by peritoneal membrane anteriorly called masochism and posteriorly by ordinary tissue with the caeca gland.
• The sperm cells escape by vasa efferent into the vas deferens and becomes extremely coiled in the anterior portion.
• Posteriorly the vas deferens becomes very much dilated to form the seminal vesicle.
• The seminal vesicles open into the urinogenital sinus and turn opens into the cloaca.
• The wall of the urinogenital sinus and become emarginated formed sperm sac.
• A pair of sacs called as siphons.
• These are located under the skin on the ventral aspect of body.
• The sacs are continued as the siphon tubes which open to the groove of the clasper of the respective sides at posterior.
• But the siphons are not connected with the genital system.
• They contain sea-water and help in the expulsion of the sperms through the clasper groove.

Female urogenital system of Scoliodon:-

Female reproductive system:-

• In female genital organ kidney has no any connection.
• The kidneys are typical accepting that the ureters unite posteriorly and open by a single urinary aperture into the urinary sinus.
• One pair of ovary and are kept in position by peritoneal folds called mesovarium.
• The shape, size and colour of the ovaries is vary and greatly according to the age of the individual.
• A pair of epitomical organs is present between the ovary and the rectal gland.
• Male Urinogenital organs Female Reproductive System 16 The oviducts are long tubes and remain united anteriorly and posteriorly.
• Posteriorly two oviducts unite and form the vagina which opens into the cloaca.
• The oviducts converge anteriorly and open into the coelomic cavity by oviducal funnel.
• At the anterior portion of oviduct dilated shell gland present.
• As Scoliodon is viviparous the posterior portion of the oviduct becomes dilated to form the uterus for the development of the young ones.
• There are seven embryos present inside one uterus of Scoliodon.
• The mucous membrane of uterus becomes separated and divided into a number of compartments like the houses an embryo.
• The eggs are large, heavily yolk and gets a coating of albumen during its transit down the oviduct.

Economic Importance Of Fishes:-

• Fishes are one of the most important group of vertebrates serving as food for human.
• They possess a great economic, nutritional, medicinal, industrial, aesthetic and religious values as well as providing employment for millions of people in the world.
• They contribute to food security in many regions of the world, providing a valuable supplement for diversified and nutritious diets.
• Consumption of fish has several health, nutritional, environmental and social advantages over other terrestrial animal meat.
• The importance of fishes can be discussed under the following headings.

Economically Food Value Fishes In Fresh Water:-

1. Food value:-

• Fish serves as an important food for human.
• Edible tissues of fish are appreciably greater than that in chicken, pig and sheep/goat.
• For example, approximately 65% of the raw weight of finfish is eaten, compared with 50% of chicken and pigs, and 40% of sheep/goat; fish are supported by water, but terrestrial animals and birds require comparatively strong bones so they spend their substantial energy into the growth of the bones, which cannot be consumed as food.
• The total estimated fish production of the world in 2012 was 158 million metric tons with a per caput consumption around 19.2 kg.
• Similarly, the total estimated fish production of Nepal in 2013/14 was 64,900 metric tons with a per caput consumption of 2.3 kg.

2. Nutritive value:-

• Fish is highly nutritious.
• It provides tasty, low calorie meal but is a good source of high quality protein.
• Fish is an almost zero-carbohydrate food, good for diabetes and other such patients.
• The protein content in fishes varies from 15-30% on wet weight basis and 60-80% on dry weight basis.
• The protein of fish is highly digestible and with well-balanced amino acids.
• Fish are low in fat and cholesterol.
• Fish is a good source of Vitamins- A, B and D and also offers a good source of calcium, iodine, fluorine, magnesium and zinc.
• Fish are rich in poly-unsaturated fatty acids containing Omega-3.
• Two poly-unsaturated fatty acids present in fish, eicosatetraenoic acid (EPA) and docosahexaenoic acid, collectively known as Omega-3, are essential fatty acids.
• They cannot be produced in human body, but are essential in the diet.
• These poly-unsaturated fatty acids can help to reduce the cholesterol level in the blood, thus minimize the risk of heart attack.

3. Medicinal value:-

• Fish is low in fat, high in protein and an excellent source of Omega-3 fatty acids.
• Regular consumption of fish can reduce the risk of various diseases and disorders.
• Some research findings indicate the following:-�Asthma:- Children who eat fish are less likely to develop asthma.�Brain and eyes:-
• Fish rich in Omega-3 fatty acids can contribute to the health of brain tissue and the retina of the eye.
• The IQ level of children whose mother consumed about 340 g fish per week during pregnancy was found higher than non-fish eaters.
• Similarly, breastfed babies whose mothers eat fish have better eyesight, perhaps due to the Omega-3 fatty acids transmitted in breast milk.�Cancer:-
• The Omega-3 fatty acids in fish reduce the risk of many types of cancers by 30 to 50 percent, especially of the oral cavity, oesophagus, colon, breast, ovary and prostate.

Cardiovascular disease:-

• Eating fish every week reduces the risk of heart disease and stroke by reducing blood clots and inflammation, improving blood vessel elasticity, lowering blood pressure, lowering blood fats and boosting good cholesterol.�Depression:-
• People who regularly eat fish have a lower incidence of depression.
• Depression is linked to low levels of Omega-3 fatty acids in the brain.�Diabetes:-
• Fish may help people with diabetes to manage their blood sugar levels.�Prematurity:-
• Eating fish during pregnancy may help reduce the risk of delivering a premature baby.
• Further, it is observed that different fishes are used as Ayurvedic medicines which help in treatment of duodenal ulcers, skin disease, night blindness, weakness, loss of appetite, cough and cold, bronchitis, asthma, tuberculosis, etc.

4.Fish products:-�A. Fish meal:-

• The dried and ground preparation of unused or trash fish is called fish meal and is a highly nutritive product that makes an excellent feed for poultry, pig, cattle and fish.
• Fish meal contains about 60-70% crude protein, 2-15% oil and 10-20% minerals.
• The protein of fish meal is highly digestible and contains all amino acids.
• It is also very rich in vitamins, calcium, phosphorous and iodine.�B. Fish oil:-
• Fish oil is of two kinds, body oil and liver oil.
• The oil extracted from the whole body of the fish is called fish body oil.
• For the extraction of body oil, the fishes are minced, steamed, and then pressed for oil recovery, then subject to filter for refine.
• It is very rich in iodine.
• The fish body oil is mostly used in manufacture of paints, varnishes, soaps, lubricants, candle, printing inks, etc.
• It is also used in dressing of leather, tanning of skin and smearing the surface of boats for longer preservation.
• It is very rich in Vitamin A and D.

C. Fish leather:-

• The coarse scaly skins of several fishes (e.g., sharks and rays) are used for manufacturing, polishing and smoothing materials in place of sand paper.
• The dried and processed skin is also used for preparing high-quality shoes, moneybags, suitcases, belts, phone cases, etc.
• Fish leather is an eco-friendly alternative to the typical exotic leathers such as crocodile and snake that threaten endangered species.

D.Fish fin:-

• The fins of the sharks and rays are used to make tasteful sauce and soups.
• It is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture.

E. Fish pearls:-

• The material obtained by scraping the silvery coating of the scales of certain fishes is used for polishing the hollow glass beds.
• These beds are then filled with wax and marketed as artificial pearls which are used as jewelry.�F. Fish insulin:- Insulin is extracted from the pancreas of large sized fishes such as sharks. Prior to the introduction of biosynthetic insulin, insulin derived from sharks and other fishes was extensively used for glycemic control in human.�

5. Biological control:-

• Many species of carnivorous and larvivores fishes prey upon insects and their larvae in water.
• These fishes can be used to control harmful insects, mosquito larvae, etc.
• Gambusia affine is a well known fish for mosquito control, hence called mosquito fish.
• Other larvivores species are Brachy danio spp., Rasbora spp., Puntius spp., Somu's spp., Colusa spp., Barillas spp., Chela spp., etc.
• They help in biological control of dengue, malaria, filaria, encephalitis, etc.
• Similarly, the herbivorous species like grass carp, tilapia, silver barb. etc.
• are used to control aquatic weeds and vegetations.

6. Sports and games:-

• Sport or recreation fishing is the fishing for pleasure or competition.
• Sport fishing can be done in a variety of ways.
• The most common form of sport fishing is done with a rod, line and hooks with baits, called angling.
• he most common sport fishes of Nepal are Sahara and rainbow trout.

7. Decorative value:-

• Many species of colored fish are kept in aquarium, oceanariums, ponds and lakes for decoration.
• The common ornamental fish species kept in aquarium in Nepal are gold fish (Crassus spp.), gourami (Colusa spp.), zebra fish (Brach danio spp.), guppy (Poe cilia spp.), fighting fish (Betta splendors), koi (Cyprinus carpi), etc.�8. Employment opportunity:-
• Fisheries and aquaculture sector provide, either directly or indirectly, a great employment opportunity for millions of people around the world.
• In 2012, about 500 million people were directly engaged in the world, part time or full time, in production of fish, either by fishing or in aquaculture.
• Fisheries and aquaculture sector in Nepal is relatively small, which provides employment to about 0.6 million people in 2013/14.

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General characters of Amphibians:-

General Characters of Amphibians:-

• Amphibians are cold blooded vertebrates which can hue on land and in water.
• Amphibians show four limbs with which they can swim in water and jump or walk on the land, (But in pada limbs are absent.)
• In Amphibians  animals exoskeleton is absent.
• But in apoda animals small cycloid scales are present.
• In Amphibians the adult animals lungs are present.
• Gills are absent. But In some urodeles the gills are present.
• Amphibians Skin is a respiratory organ.
• The Amphibians skull is dicondylic.
• Amphibians Ribs are absent.
• In Amphibians The body divisible into head and trunk Tail is present in, urodele animals.
• Amphibians  Digestive system is well developed.
• A well developed liver Is present

• External ear is absent.
• Middle and inner ears are present, the middle ear columella Auris Is present.
• Amphibians Heart is 3 chambered with 2 auricles and 1 ventricle.
• The blood contains R.B.C.
• They are nucleated.
• They contain hemoglobin.
• Blood vascular system contain hepatic and renal portal systems.
• Amphibians Kidneys are mesonephric. Urinary bladder is present.
• It stores urine.
• Central nervous system is well developed.
• The brain occupies completely the cranial cavity.
• The brain is divided into fore, mid and hind brains.
• Brain continuous as spinal cord.
• 10 pairs of cranial nerves will arise.
• Sexes are separate.
• Male and female can be identified - Sexual dimorphism.
• In Amphibians the life history a larva stage may be present.
• Amphibian Eggs are telolecithal, Cleavage is holoblastic unequal.

Classification of Amphibia:-

The Amphibians are divided into three orders.

The classification of amphibia is given below:-

1. Apoda (Gymnophiona):-

• Apoda means “without legs”.
• These are limbless organisms with scales on their body.
• They are also known as “blind-worms” because their eyes are covered by skin or bone.
• The tentacles on their head are the chemosensory organs that help them to detect the underground prey. E. g. , Caecilians
• They possess venom glands.
• They secrete mucus to reduce water loss.

2.Urodela (Caudata):-

• These are the organisms with a tail.

• The body is elongated with four equally sized limbs.
• The skin is smooth with poison glands.
• Fertilization is internal.
• They feed on insects and worms. E g., Salamanders
• They are found under leaf litter, in the soil, or in water.
• In the southern US, they reproduce primarily in winters.
• Very little differences between male and female.
• Spermatophores are utilized for internal fertilization.
• They possess hidden gills.

3.Anura (Salientia):-

• There are around 3400 species of Anura in the world.
• They have four limbs. The front limbs are elongated and modified to jump.
• The head and trunk are fused together.
• The tail is present only in the larval stage and is lost in the adults.
• Fertilization is external and the eggs are laid in water. Eg., frogs and toads.

Different Types of Parental Care in Amphibia:-

Parental care in Amphibians:-

Definition:-

Looking after the eggs or young until they are independent to defend from predators, is known as Parental care.

• Protection by nests, nurseries Direct carrying by parents.

1. Selection of site: –

• Many amphibians lay eggs in protected moist microhabitats on land.
• Many tropical frogs and toads lay eggs on land near water.
• Many tree frogs lay their eggs not on land but on leaves and branches over hanging water.

E.g. Rhacophorus, Hyles.

2. Defending eggs or territories:-

• Males of green frog Rana claimants and other species maintain territories and attack small intruders to defend eggs. Male or female even guards the eggs.
• Protection by nests, nurseries or shelters

3. Direct development: –

• In some terrestrial or tree frogs, such as Arthroleptid and Hyles, the eggs hatch directly into little frogs thus avoiding larval mortality.

4.Foam nests:– Many amphibians convert copious mucous secretions into nests for their young.

5. Mud Nests: – In Brazilian tree frog Hyla fabre , the male digs a little crater-like hole or nursery in mud in shallow water, in which the female lays her eggs.

6. Tree nests: – The south American tree frogs Phyllo medusa hypochondrial, lays eggs in a folded leaf nest with margins glued together by cloacal secretion.

1. Coiling around eggs: - in Congo eel, Amphiumid and certain caecilians, the female lays large eggs in burrows in damp soil and carefully guards them by coiling her body around them until they hatched.

2. Transferring tadpoles to water: – some species of small frogs in both tropical Africa and South America, the hatching tadpoles fasten themselves to the back of one of the parent with their sucker like mouth and transported to water.

3. Eggs glued to body: – Many amphibians, instead of remaining with the eggs, carry the eggs glued to their body. Eg. Dusky salamander DIRECT CARRYING BY PARENT

4. Eggs in back pouche:- In marsupial frogs or toads, the female carries the eggs on her back, either in an open oval depression, a closed pouch or in individual pockets.

5. Vivi parity: – Some anurans are ovoviviparous. They retain eggs in the oviducts and the females gives birth to living young.

Hibernation and Aestivation in Frog:-

Hibernation:-

 or “winter sleep” is the state of inactivity or low metabolic process performed by the animals during winters. 

Aestivation:-

 or “summer sleep”, on the other hand, is the low metabolic process by the animals during summers.

Aestivation:-

• Aestivation occurs in animals living in deserts and tropical regions.
• This is done to protect themselves from hot and dry climate, and due to the scarcity of food water.
• This can be seen in earthworms, molluscs, arthropods, reptiles. and amphibians.
• A lungfish can aestivate and survive without water for three years.
• The sole motive of aestivation is to prevent water loss or dehydration and to save energy.

Hibernation:-

• Hibernation is the condition in which the animals go dormant during winters by lowering their metabolic activities.
• This can be seen in reptiles, fish and amphibians.
• To combat the problem of food shortage during hibernation, these animals eat a lot of food and store in the form of excess fat.
• This is supplied in the form of energy while sleeping.

UNIT-III

General characters of Reptiles:-

General Characters Of Reptiles:-

•  Reptiles are terrestrial (or) aquatic animals.
• The body of Reptiles is covered with horny scales.
• In Reptiles Skin is dry.
• Glands are absent in the skin of Reptiles.
• Four limbs are present.
• They are pentadactyl (having 5 fingers).
• Skull occipital incompletely.
• In Reptiles Vertebrae are gastrocentrous.
• In Reptiles Ribs from a true sternum.
• Respiration is carried on by the lungs.

• In Reptiles Heart is divided into two auricles and ventricle is divided into2 chambers incompletely.
• Right & left aortic arches are completely formed.
• Red blood corpuscles are nucleated in Reptiles.
• In Reptiles Kidneys are meta nephric.
• Each kidney is provided with separate ureter.
• In Reptiles Twelve pairs of cranial nerves are seen.
• Cloaca is present.
• Fertilization is internal.
• Eggs are laid on land.
• In Reptiles Extra embryonic membranes are present during the development of the embryo.

Classification of Reptiles:-

The class Reptiles is differentiated into three major sub-classes:-

1. Anapsida
2. Parapsida
3. Diapsida

1. Anapsida:-

• The dermal bones form a complete roof over the skull with no temporal fossae.
• These are sub-divided into Cotylosauria and Chelonia.
• Modern chelonians are classified according to the method of retracting the head in the shell.
• Turtles, tortoises, and terrapins belong to this group.

2. Parapsida:-

• These reptiles possess one temporal fossa present high up on the skull.
• Protosaurs, Nothosaurs, Placodonts showed this type of skull.
• The two largest groups among these were- Ichthyosaurs and Plesiosaurus.
• These became extinct at the end of the Cretaceous period when several other reptiles including dinosaurs died.

3. Diapsida:-

• There are two temporal vacuities in the skull.
• They are diverse of all reptiles.
• The dinosaurs and pterosaurs are included in this group.
• These are divided into two major groups- Archosauria and Lepidosauria.
• Eg., Crocodiles, Chameleon

Groups of Reptiles:-

The class Reptile is further divided into different groups known as orders:-

​

Extinct groups of class Reptilia:-

1. Ichthyopterygia
2. Lepidosauria
3. Archosauria
4. Synapsida

1. Ichthyopterygia:-

• This group had one temporal fossa place high up on the skull.
• The two largest groups belonging to this sub-class are Ichthyosaurs and Plesiosaurs.
• Eg., Ichthyosaurus

2. Lepidosauria:-

• These were all the lizard-like reptiles.
• They had two temporal vacuities in the skull.
• Eg., Youngina,

3. Archosauria:-

• The skulls were diapsid.
• Some were bipedal which gave rise to birds.
• They also gave rise to dinosaurs.
• Eg., Brontosaurus

4. Synapsida:-

• They had one temporal fossa on the lower side of the skull.
• These were the most dominant group of reptiles during the Permian period.
• The surviving Plesiosaurs in the Mesozoic era gave rise to mammals.
• The rest were replaced by dinosaurs. Eg., Plesiosaurus.

• If the small scales are present on the belly and back, it is a non-poisonous snake.
• If the belly scales are not broad enough to extend right across it, it is a non-poisonous snake.

• If broad plates cover the entire width of the belly, it is poisonous or non-poisonous.
• If small scales are present on the head, it is poisonous and a viper.
• If small scales or shields are present on the head and a pit lies between the eye and the nostril, it is poisonous and a pit-viper.

• If dorsal side of the head has both small scales and large shields, the snake may or may not be poisonous.

• If the third supra labial scale touches the eye and the nostril, the snake is a cobra or a coral snake.
• If the neck is with hood and markings, it is cobra.
• If neck is without hood and coral spots are present on the belly, it is a coral snake.
• Both cobra and coral snakes are poisonous.
• If vertebral (scales on the middle of the back) are hexagonal and larger than other scales over the back and the fourth infra-labial scale is the largest, it is poisonous and a krait.
• If the snake has small scales and large shields on the head but does not have the characters of cobra, coral-snake or krait, then it is non poisonous. 

Difference between poisonous and non-poisonous snakes:-

Images of Biting Mechanism in Snakes:-

Biting Mechanism in snakes:-

There are four distinct phases when a poisonous snake bites:-

1. The strike.
2. opening of the mouth and elevation of the fangs.
3. closing of the jaws and the injection of venom.
4. retraction of the fangs.

1. The strike: –

• In this phase the snake throws itself forward with great rapidity and violence, the distance covered not generally exceeding one-third of its length.
• Vipers strike with greater velocity than the colubrid, some of which especially the hooded species raise the head from the ground thus compensating to some extent for the limited mobility of the fangs.

2.Opening of the mouth and elevation of the fangs:-

• Most poisonous snakes commence the strike with closed jaws, but as the head approaches the victim the mandibles are depressed by a rapid contraction of the digastric, cervical-mandibular and vertebra-mandibular muscles and simultaneously the fangs are elevated or rotated forward by the forward swing of the pterygoid-palatine-transverse arch produced by the contraction of the sphenoid parieto-pterygoid muscles.
• The fangs of the Colubrid are invariably grooved and are generally shorter than those of the viper, and their capacity for forward rotation is much more limited.
• The degree of elevation from extreme retraction to maximal protraction varies from 10°- 15o to 450 -500 in different species.

• Each pterygoid-palatine-transverse arch acts as a single entity, and then the protractor muscles of the palate draw the endo-pterygoid forward, they invariably bring with it the palatine bone and the recto-pterygoid which impinges on the posterior arm of the maxilla, driving the maxilla forwards and upwards on the articulating surface of the prefrontal.
• This produces a variable degree of elevation and forward rotation of the fangs, which are ankylosed to the inferior surface of the maxilla; its extent can be judged by the angle formed at the ectopterygoid maxillary junction which, in the resting position, forms a straight line.
• In these snakes, the smaller the maxilla the greater the forward movement of the pterygoid-palatine-transverse arch and the greater the degree of forward projection of the fangs.
• This mechanism differs from that of the vipers in which the movement of the maxilla on the prefrontal is a 9 true rotary one and not a forward and upward sliding movement as described above.

3. Closure of the mouth and the injection of venom:-

• Closure of the jaws follows, a result brought about by the simultaneous contraction of the anterior, middle and posterior temporal muscles which strongly elevate the mandibles.
• In the colubrid the venom gland is also compressed by the superior and inferior portions of the anterior temporal muscles, producing torsion on its capsule with the expulsion of venom from the gland along the duct, the papilla of which becomes approximated to the groove at the base of the fang, but in certain Australian species venom may sometimes be observed to spurt a considerable distance during a snap bite at a time when no object is actually being bitten.
• In the vipers there is an entirely different 10 anatomical arrangement of muscles acting on the venom gland; expulsion of its contents is instantaneous and independent of fixation of the lower jaw.

4. Retraction of the fangs:-

• Immediately following the insertion of the fangs, and actually accompanying the discharge of venom, contraction of the retractor muscles which operate on the pterygote-palatine-transverse arch occurs, dragging the elevated fangs downwards and backwards through the tissues.
• Though the four stages including the inoculation of venom are described separately, they occur in nature as a series of rapidly coordinated movements, several lethal doses being injected in a fraction of a second in some instances especially with the vipers.

Images of Snake Venom:-

• Some of the proteins in snake venom have very specific effects on various biological functions including blood coagulation, blood pressure regulation, and transmission of the nervous or muscular impulses, and have been developed for use as pharmacological or diagnostic tools, and even useful drugs.

Types of Snake Venom:-

As explained in the introduction venomous snakes can be classified into three classes the snake venoms for two are explain below:-

• The elapines, short front fangs (Proteroglyphs) snakes, which include the cobra, mamba, and coral snakes, their venom is neurotoxic (nerve toxins) and paralyses the respiratory center.
• Animals that survive these bites seldom have any sequelae (aftereffects of the snake bite such as tissue damage).
• The two families of viperine, the true vipers (e.g., puff adder, Russell's viper, and common European adder the only venomous snake in the UK) and the pit vipers (e.g., rattlesnakes, copperhead, and fer-de-lance).
• Viperine snakes have long, hinged, hollow fangs; they strike, inject venom

(a voluntary action), and withdraw.

• Many bites by vipers reportedly do not result in injection of substantial quantities of venom.

Importance of Snake Venom:-

• Viperine venom is typically hemotoxic (blood toxins), necrotizing (death of tissue), and anticoagulant (preventing the blood from clotting), although a neurotoxic component is present in the venom of some species, e.g., the Mojave rattlesnake
• There are approximately 20 types of toxic enzymes found in snake poisons throughout the world known to man.
• Although no venomous snake has all of these toxins, most snakes employ between six to twelve of these enzymes in their venom.
• Each of these enzymes has its own special function.
• Some aid in the digestive process, while others specialize in paralyzing the prey.

This is a list of various toxins that have been identified in snake venom:-

• Proteolytic enzymes
• Phosphomonoesters
• Arginine ester hydrolase
• Phosphodiesterase
• Thrombin-like enzyme
• Acetylcholinesterase
• Collagenase RNase
• Hyaluronidase
• DNase Phospholipase A2
• (A)5'-Nucleotidase
• Phospholipase B
• L-Amino acid oxidase
• Phospholipase
• Lactate dehydrogenase
• Adenosine triphosphatase

Images of Aves:-

General characters of Aves:-

General Characteristics of Aves:-

• Birds are warm-blooded animals.
• Their forelimbs are modified into wings.
• They have well-developed flight muscles that help during the flight.
• Their hind limbs are adapted for walking, hopping, perching, grasping, wading and swimming.
• There are epidermal scales on their legs.
• The endoskeleton is bony with long hollow bones filled with air cavities.
• known as pneumatic bones.
• Their spindle-shaped body minimizes resistance of the wind.
• The feathers help in preventing heat loss and reduce air friction by providing passage to the air.
• There is no skin gland except the oil gland.
• The lower and upper and jaws are modified into a beak.
• They have no teeth.

• They have sharp eyesight.
• The alimentary canal has a crop and a gizzard.
• The crops help in softening food, and the gizzard helps in crushing the food.
• Pigeons and other seed-eating birds lack a gall bladder.
• They have spongy and elastic lungs for respiration.
• The special vocal organ called syrinx is present at the base of trachea.
• Their heart is four-chambered.
• RBCs are oval, nucleated and biconvex.
• 12 pairs of cranial nerves are present.
• They have a single ovary and oviduct on the left side
• All the birds are oviparous and exhibit sexual dimorphism.
• The eggs have four embryonic membranes- amnion, chorion,  allantois, and yolk sac.

Flight Adaptation in Birds:-

Flight Adaptations in birds:-

There are two types of flight adaptations in birds:-

1. Morphological Adaptations.
2. Anatomical Adaptations.

1. Morphological Adaptations:-

1. Body Contour:-

• The birds have a spindle-shaped body to offer less air resistance during flight.
• This helps the birds to conserve energy and become more efficient at flying.

2. Compact Body:-

• The body of a bird is compact, dorsally strong and ventrally heavy to maintain equilibrium in the air.
• Their wings are attached on the thorax, the light organs like lungs and sacs are positioned high, the heavy muscles placed centrally are other features that help in flight.

3. Body Covered With Feathers:-

• The feathers are smooth, directed backwards, and closely fitting which make the body streamlined and reduce friction during flight.

• It lightens the body weight and protects it from the effect of environmental temperature.
• They also have a wide surface area for striking the air.
• Feathers add to the body buoyancy.
• It insulates the body and prevents any loss of heat from the body.
• This helps the birds to bear low temperatures at higher altitudes.

4. Forelimbs Modified into Wings:-

• The forelimbs are modified into wings, which is the only organ of flight.
• These consist of a framework of bones, muscles, nerves, feathers, and blood vessels.
• The wings have a large surface area.
• They also support the bird in the air.
• The wings have a thick, strong leading edge with a concave lower surface and a convex upper surface.
• This helps in increasing the air pressure below and reducing the air pressure above.
• Thus the bird can fly upward and forward during flight.

5. Mobile Neck and Head:-

• The birds have a long and flexible neck, which helps in the movement of head important for various functions.
• They possess a horny beak which helps them to pick the grains and insects while feeding.

6. Bipedal Locomotion:-

• The anterior part of the body of a bird helps in taking off during flight.
• The anterior part of the body also helps birds to land.
• The hindlimbs help in the locomotion on land.
• They can support the entire body weight of a bird.

7. Perching:-

• When a bird sits on the branch of a tree, its toes wrap around the twig.
• This is known as perching.
• The muscles are so well-developed that a bird can sleep in that position without falling.

8. Short Tail:-

• The tail bears long feathers that spread like a fan and function as a rudder during flight.
• They also help in balancing, lifting, and steering while flying and perching.

2. Anatomical Adaptations:-

1. Flight Muscles:-

• The well-developed muscles control the action of the flight muscles.
• It weighs about 1/6th of the entire bird. The flight muscles are striated.
• The muscles on the wings are large.
• Other muscles help the above muscles in functioning.

2. Light and Rigid Endoskeleton:-

• The birds have a very stout and light skeleton.
• The bones are hollow, filled with air sacs.
• They are provided with a secondary plastering to increase their rigidity.
• The bones are fused and lack bone marrow.
• The birds lack teeth.
• The thoracic vertebrae are fused except for the last one.
• This plays an essential role in the action of wings striking the air.

3. Digestive System:-

• The birds have a very high rate of metabolism.
• Therefore, food digests rapidly.
• The length of the rectum is reduced because of the minimum undigested waste.
• They have no gall bladder which reduces the weight of the bird.

4. Respiratory System:-

• The respiratory system of birds is designed in such a manner that the food is oxidized rapidly and a large amount of energy is liberated.
• Since the metabolism rate is higher, a large number of oxygen molecules are required by the body.

• For this, the lungs are provided which occupy the entire space between the internal organs.

5. Circulatory System:-

• Rapid supply of oxygen is required by the blood due to rapid metabolism rate in birds.
• Therefore, birds require an efficient circulatory system.
• Birds have a four-chambered heart that performs double circulation.
• This prevents the mixing of oxygenated and deoxygenated blood.
• Also, the birds contain a large amount of hemoglobin in their red blood cells, which helps in the quick aeration of body tissues.

6. Warm Blooded:-

• The temperature of the body of a bird remains high and does not change with the change in the environment.
• This facilitates the birds to fly at very high altitudes.

7. Excretory System:-

• The nitrogenous waste is converted to less toxic organic compounds such as uric acid, and urates.
• They have no urinary bladder.
• The uriniferous tubules efficiently absorb water.

Migration in Birds:-

Migration in Birds:-

Definition:-

• The word “migration” has come from the Latin word migrara which means going from one place to another.
• Many birds have the inherent quality to move from one place to another to obtain the advantages of the favorable condition.
• In birds, migration means two-way journeys—onward journey from the ‘home’ to the ‘new’ places and back journey from the ‘new’ places to the ‘home’.
• This move­ment occurs during the particular period of the year and the birds usually follow the same route.

  Types of Bird Migration:-

• All birds do not migrate, but all species are subject to periodical movements of vary­ing extent.
• The birds which live in northern part of the hemisphere have greatest migra­tory power.

Migration may be:-

(i) Latitudinal,

(ii) Longitudinal,

(iii) Altitudinal or Vertical,

(iv) Partial,

v) Total,

(vi) Vagrant or Irregular,

(vii) Seasonal,

(viii) Diurnal and

1. Latitudinal migration:-

• The latitudinal migration usually means the movement from north to south, and vice versa.
• Most birds live in the land masses of the northern temperate and subarctic zones where they get facilities for nesting and feeding during summer.
• They move towards south during winter.
• An opposite but lesser movement also occurs in the southern hemisphere when the seasons are changed
• Cuckoo breeds in India and spends the summer at South-east Africa and thus covers a distance of about 7250 km.
• Some tropical birds migrate during rainy season to the outer tropics to breed and return to the central tropics in dry season.
• Many marine birds also make considerable migra­tion
• It covers a distance of 1300 km.
• Penguins migrate by swimming and cover a considerable distance of few hundred miles.
• Sterna paradises (Arctic tern) breeds in the northern temperate region and migrates to the Antarctic zone along the Atlantic.
• It was observed that Sterna covers a distance of 22 500 km during migration!

2. Longitudinal migration:-

• The longitudinal migration occurs when the birds migrate from east to west and vice- versa.
• Starlings (Sturnus vulgaris), a resident of east Europe and west Asia migrate towards the Atlantic coast.
• California gulls, a resident and breed in Utah, migrate westward to winter in the Pacific coast.

3. Altitudinal migration:-

• The altitudinal migration occurs in moun­tainous regions.
• Many birds inhabiting the mountain peaks migrate to low lands during winter.
• Golden plover starts from Arctic tundra and goes up to the plains of Argentina covering a distance of 11 250 km.
• Birds migrate either in flocks or in pairs.
• Swallows and storks migrate a distance of 9650 km from northern Europe to South Africa.
• Ruff breeds at Siberia and travels to Great Britain, Africa, India and Ceylon thus travelling a distance of 9650 kilometers.

4. Partial migration:-

• All the members of a group of birds do not take part in migration.
• Only several members of a group take part in migration.

• Blue Jays of Canada and northern part of United States travel southwards to blend with the sedentary populations of the Southern States of U.S.A.
• Coots and spoon bills (Plata lea) of our country may be example of partial migration.

5. Total migration:-

• When all the members of a species take part in the migration, it is called total migration.

6. Vagrant or irregular migration:-

• When some of the birds disperse to a short or long distance for safety and food, it is called vagrant or irregular migration.
• Herons may be the example of vagrant or irregular migration.
• Other examples are black stork (Ciconia nigral), Glossy ibis (Plegadis falcinellus), spotted eagle (Aquila clang), and bee eater (Merope a piaster).

7. Daily migration:-

• Some birds make daily journey from their nests by the influence of environmental factors such as temperature, light, and humidity also.
• Examples are crows, herons and starlings.

8. Seasonal migration:-

• Some birds migrates at different seasons of the year for food or breeding, called seasonal migration, e.g., cuckoos, swifts, swallows etc.
• They migrate from the south to the north during summer.
• These birds are called summer visitors.
• Again there are some birds like snow bunting, red wing, shore lark, grey plover etc.
• which migrate from north to south during winter.
• They are called winter visitors.

Nocturnal and Diurnal Flight:-

1. Diurnal migration:-

• Many larger birds like crows, robins, swal­lows, hawks, jays, blue birds, pelicans, cranes, geese, etc.
• Migrate during daytime for food.
• These birds are called diurnal birds and gene­rally migrate in flocks.

2. Nocturnal birds:-

• Some small-sized birds of passerine groups like sparrows, warblers, etc.
• migrate in darkness, called nocturnal birds.
• The darkness of the night gives them protection from their enemies.

UNIT-IV

General characters of Mammals:-

• Mammals are warm blooded animals.
• The body is covered by hairs.
• The skin contains two types of glands.
• They are Sweat glands and Sebaceous glands.
• Sweat glands are useful in excretion.
• Sebaceous glands produce Sebum.
• This will keep the skin soft & smooth.
• In Mammals mammary glands are present.
• They are functional in female.
• They are modified sebaceous glands.
• But in prototherians they are modified sweat glands.
• External ears are present (Pinnae).
• The internal ear contains highly coiled hearing organ called organ of Corte or Cochlea.

• External Nostrils open into the internal nostrils.
• They open into pharynx.
• The teeth are Heterodont.
• Types of dissimilar teeth are present.( Incisors, Canines, Premolars, molars.)
• The teeth are diphyodont. (Two sets of teeth are developed).

• The codont teeth are present in sockets of jaw bones.
• The skull has two occipital condyles.
• Hence it is called dicondylic skull.
• The lower jaw is made by single bone called dentary.
• Each vertebra is composed of one centrum and two epiphyses.
• In the neck of Mammals seven cervical vertebrae are present.
• The ribs are double headed, capitulum, Tuberculum.
• The fore and hind limbs bear digits which will not be more than five.

• The upper is thoracic cavity and lower abdominal cavity.
• Heart shows 4 chambers.
• Only left aortic arch is present.
• Non-nucleated R.B.C. is present.
• Brain is well developed.
• In brain 4 optic lobes are present.
• Cerebrum is well developed.
• Metanephric kidney is present.
• In the nephron Henley loop is present.
• Penis is present.

• Male and females are separate.
• They give birth to young ones.
• But in Monotrems they lay eggs.
• In the uterus the fetus grows.
• This period is called Gestation period.
• Fetus is nourished by placenta through placental connection.

Classification of Mammals:-

Classification Of Mammals:-

• Mammalia has the largest class in the animal kingdom.
• Based on their reproduction, they are classified into three subclasses:-

1. Eutheria

2. Metatheria

3. Prototheria

1. Eutheria:-

• Mammals under this subclass give birth to young ones.
• The young ones are developed inside the mother and derive nutrition through the placenta from the mother.
• Further more, it consists of 19 orders, few of which are:-

2. Metatheria:-

• Mammals belonging to this sub-class give birth to immature young ones, hence they stay in their mother’s pouch until they mature.

For e g .,Marsupials and Kangaroos.

• They are divided into seven different orders:-

3. Prototheria:-

• Also known as Monotremes, the sub-class Prototheria consists of egg-laying mammals.
• It has one order having 6 species

Order: Monothematic

Example: Duckbilled platypus, Echidna

General Classification of Mammals:-

• The scientists have also classified the mammals on a general basis which makes it easy to learn about the mammals and their distinguishing characteristics.

RAT

External Characters Of Rat :-

• The rat has a cylindrical and soft body, gradually tapering towards both the ends.
• this type of body is well suited for running in narrow burrows or squeezing through small holes and crevices.
• Its body has a typical mammalian form.
• It is divisible into head, neck, trunk and tail.

1)The head :-

(1) More or less conical in shape, the head is slightly compressed internally. It tapers towards the anterior end forming a pointed snout.

(2) At its front end, the head bears a pair of oblique slits, the external nostrils, and a narrow mouth bounded by soft upper and lower lips.

(3) The upper lip is cleft in the middle, so that the front teeth are exposed even when this is closed.

(4) On either side of the nostrils, the snout bears long and stiff hair called vibrissae or whiskers. These are sensitive hair grouped into four types according to their position.

1)Mystical – Located on the upper lip the anterior ones are short but they gradually increase in length posteriorly.

2)Superciliary – Short vibrissae placed above the eye.

3)Genal – a single vibrissa lying below the eye.

4)Submental – these are numerous vibrissae located on the chin.

5)The eyes are situated one of either side of the head in such manner that they diagonally forward and on the sides.

6)Each eye is protected by the upper and lower eyelids. Both of them are bordered with eyelashes at an the inner angle of each eye, there is a transparent membrane often called the nictitating membrane, it forms the third eyelid as compared to the birds and frogs,

it is extremely reduced to a plica semilunaris.

7) The colour of eye is due to the pigmented membrane that lies below the transparent corned.

8) This coloured portion is the iris. It has a central opening, the pupil, through which light enters the eye.

9. Each pinna is a large movable flap meant to catch concentrate & direct the sound waves into the external auditory meatus a passage leading to the middle ear.
10. This meatus lies at the base of the pinna.

2)The Neck :-

(1)The neck is short.

(2)It joins the head to the trunk, it allows free movement to the head, so that it can be turned in any direction to see the surroundings.

3)The Trunk :-

(1)The trunk is elongated.

(2)It is divisible into the anterior thorax & the posterior abdomen.

(3)The thorax is supported by ribs & a breast bone; the abdomen is however soft.

(4)In the female rat the ventral surface bears 10-12 nipples or teats arranged on two unevenly spaced rows.

(5)Three pairs are on the thoracic region & the other pairs on the abdominal one.

(6)These teats bear the external openings of the milk or mammary glands the teats in the male are very small and often undeveloped.

4)The Tail :-

(1)At the posterior end of the trunk is a tail; it is as long as or longer than the trunk.

(2)The cylindrical tail gradually tapers towards the hind end.

(3)It is covered over by overlapping epidermal scales arranged in rings.

(4)The rat has about 210 such rings on the tail from below the edges of these scales the hairs on the tail project out.

(5)The tail is much used as a balancing organ.

(6) The anus is situated at the base of the tail on the ventral side in both the sexes.

(7) In the male however, the anus is somewhat obscured from view by a pair of scrotal sacs.

(8) The presence of the scrotal sacs is peculiar to mammals only.

(9) The testes or male reproductive organs are lodged inside these sac. In front of these sacs a common urinogenital apertures can be marked at the tip of the retractile penis.

(10)The latter is enclosed in a loose sheath of skin called prepuce.

(11)In the female the urinary and genital openings are separate.

(12)They lie anterior to the anus.

(13)A transverse slit – like female genital opening called vulva is situated in front of the anus.

5)The Limbs :-

(1)There are two pairs of limbs attached to the trunk.

(2)They are set well apart.

(3)The anterior pair, or the forelimbs are shorter while the posterior pair or the hind limbs are longer.

(4)The pairs are also flexed that the body is slightly raised above the ground the fore limbs are shows three part –

(1) the upper arm or brachium (2) the fore arm or ante-brachium & (3) the hand or manus.

(5)The hand bears four digits each ending in a curved claw.

(6)It is represented by a small nodule’s it bears a flattened nail-like claw.

(7)The foot bears five toes ending in curved claws the hallux or the first digit is much shorter than the others.

(8)The head, neck, trunk & limbs have a uniform covering of short hairs of definite pigmentation.

(9)The colour of the rat depends upon the colour of the hair.

(10)The pinnae & feet are without hair.

Digestive System Of Rate :-

• The digestive system of a rat consists of its alimentary canal with its associated mesenteries and glands.
• The alimentary canal is a continuous tube that starts anteriorly at the mouth and ends posteriorly at the anus the following regions.

• Mouth, buccal cavity, pharynx, Oesophagus stomach, small intestine, large intestine ending in the anus the gland associated with the canal are the salivary glands liver & pancreas.

1)Mouth :- The head shows more or less a pointed snout. The mouth is opening at this narrow end bounded by the upper & lower lips with the corresponding upper & lower jaws. When the mouth or the buccal cavity is seen.

2)The buccal cavity :- This cavity lies between the mouth and the pharynx. It is supported by the jaws the upper jaw is fixed while the lower jaw is movably articulated with the skull. Both the jaw bear teeth the jaw & teeth separate the buccal cavity into a median oral cavity and a peripheral vestibule. The latter is bounded by jaws internally and by lips and cheeks externally. At the base of the tongue numerous serous glands are present near the circumvallate papilla their short ducts open at the base of the groove. Small lobules of mucous glands are present laterally and dorsally; their ducts open directly on the surface of the tongue.

Teeth :- The teeth of a rat, like those of other mammals, are thecodont the are set in sockets of the jaw bones. They are also heterodont lie all of them are not alike.

3)Pharynx :- The buccal cavity leads posteriorly to the pharynx, it is the region between the oral cavity & the oesophagus, as well as between the nasal cavity & the trachea in fact it is a region common to both the digestive & respiratory systems. As mentioned above the pharynx consists of three areas :

(1)Nasopharynx lying above the soft palate.

(2)Oropharynx lying pharynx lead two tubes, oesophagus and trachea.

4)Oesophagus :- It is a narrow but dilatable, straight part of the alimentary tract. It connects the pharynx with the stomach, it runs back through the neck & chest. Anteriorly the oesophagus lies dorsal to the larynx or voice box; in the neck region. It lies parallel to the trachea.

In the thoracic region it lies dorsal to the heart and in between the lungs. The wall is the oesophagus is muscular. The mucous membrane consists of stratified squamous epithelium. The membrane is thrown into longitudinal folds. There is a longitudinal layer of muscles on the outer side & a circular layer of muscles on the inner side. These act alternately & antagonistically. Their actions produce undulating movements called peristaltic movement. In its mucous membrane there are no special glands but a large number of goblet cells secrete mucus.

5)The Stomach :-The stomach lies on the left side of the abdominal cavity close below the diaphragm. It is a large sac showing externally a division into two distinct portions- a thin walled translucent portion on the left side, the cardiac portion & a muscular opaque portion on the right side, the pyloric one. Stomach of rat region – show distribution of spectral glands, these two region differ internally too.

The cardiac portion is smooth & free of folds whereas the lining of the pyloric region is folded. Internally the stomach shows two distinct regions-

(1)the non-glandular region near the entrance of the oesophagus & a part of the cardiac region.

(2)the glandular part including the lower part of the cardiac region called fundus & the pyloric region.

6)Small intestine :-The small intestine of rat is about six times the length of its body. It is approximately uniform in diameter; it is looped and coiled. The first part of the small intestine forms of loop extending towards the right side. It is the duodenum. It encloses the diffuse pancreas in its arms. The rest of the intestine is a long narrow & coiled part, the ileum the duodenum receives a common bile duct.

It formed by the bile duct & numerous small pancreatic ducts. The wall of the small intestine is rather thin; the muscular layer is not so thick as in the stomach. The mucosa of the small intestine is raised into numerous, delicate, finger-like projections.

7)Large intestine :-

The small intestine is followed by the large intestine at the junction of the two is a blind outgrowth called caecum.

8)Caecum:- is present at the junction of ileum and colon.

It contains cellulose digesting bacteria� 9)Colon:- it absorbs water from undigested food.� 10)Rectum:- Stores undigested food and forms its pellets.� 11)Anus:- Egestion of undigested food.

Respiratory System Of Rat :-

• The transport of oxygen from the surrounding atmosphere & conveyance of CO₂ and water takes place with the help of blood.
• Even though the actual release of energy takes place in the cells of the living tissues, a set of organs concerned with the exchange of gases forms the respiratory system of the animal.
• It consist of a pair of lungs connected to the exterior by the respiratory passages, the latter comprise the nasal cavities, the pharynx, the larynx, the trachea & bronchi.

1)Nasal Cavities:-

The external nares or nostrils lead to the nasal chamber. The latter is divided by the nasal septum into right & left portions called the nasal cavities. This septum is cartilaginous anteriorly but its posterior part is bony. In rate the nostrils lie on a region of naked skin, above the upper hare-lip. This region in healthy rate, is moist & cool within the nasal much space is occupied by the turbinal bone (scroll-like maxilla – turbinals & ethmoturbinals) these bones are covered over by mucous membrane lining the nasal cavities. It is kept moist by the secretion of numerous glands present in the mucous membrane. In this epithelial lining of the nasal region. Olfactory nerve ending are unevenly distributed, the membrane moistens the air breathed in and warms it to the body temperature.

The nasal cavities together join to form a large internal or posterior naris which opens into the nasus-pharynx.

2)The Pharynx:-As noted before it is divided into the nasus-pharynx above the palate, the oropharynx below the palate & the laryngopharynx behind the buccal cavity. Thus pharynx consists of three regions; the nasopharynx, anterodorsally, the oropharynx antero-ventrally & the laryngopharynx posterior-ventrally. The oropharynx & laryngopharynx are not distinctly demarcated. The former is the portion of the pharynx ventral to the soft palate. The former is the portion of pharynx it continuous with both the oropharynx & nasopharynx, the oesophagus and larynx open into this region.

3)Larynx:-The larynx or voice box is the anterior enlarged part of the trachea. It communicates with the pharynx by the opening called glottis. An antero-ventral flap forms a lid-like epiglottis. This helps to guide the food, past the glottis, it forms a sort of a value not to allow the food to enter the trachea. It is supported by four cartilages, these include a large, shield shaped thyroid cartilage antero-ventrally, a ring-shaped cricoid cartilage lying

posterior to it; this encircles the larynx. When the vocal cords are in a relaxed condition. The air passes through the larynx easily & without producing any sound. The pitch of this sound varies according to tension & the stretched condition of the cords, the rat produces a variety of sounds.

4)Trachea:-The trachea (wind-pipe) is a long tube extending throughout the neck. It lies ventral to the oesophagus & is supported by C-shaped cartilaginous rings, whose dorsal portions are incomplete. The soft dorsal region of the trachea lies against the oesophagus. The cartilaginous rings give rigidity & flexibility to the elastic walls of the trachea. They help to keep the lumen of the trachea in an open & unclasped condition. The trachea extends into the thorax & divides to form two bronchi.

5)Bronchi:-The two bronchi, right and left, lead to the respective lungs. The bronchi are smaller and are supported by complete cartilaginous rings. Each bronchus while entering the lung

divides into secondary bronchi in the substance of the lungs these further subdivide to form tertiary bronchi & bronchial tubes. The finest branches are called bronchioles. The trachea, bronchi & bronchioles are all lined internally by a ciliated mucous membrane. It also contains a large number of goblet cells. These secrete mucus in which dust particles that might have entered the lungs & the respiratory passages are caught. The ciliated lining slowly moves the mucus away the from the lungs, thus preventing them to accumulate in the lungs.

6)Lungs:-The rat has a pair of lungs. The two lungs lie in the thorax on either side of the heart. Each lung lies in its own pleural cavity. The two pleural cavities are separated by a mediastinal septum; they form a major part of the thoracic coelom. The left lung consist of a single lobe whereas the right lung is divided into four smaller lobe. These are anterior middle, posterior & the postcaval lobes. Each lung is a pink colored spongy bag. Its internal

cavity is greatly subdivide to sacs, on the walls of which microscopic pockets called alveoli are present, the blood capillaries lie in close contact with the thin walls of the alveoli.

Physiology of Respiration:-

The process of respiration mainly consist in the release of energy. This is brought about by the breaking down of complex food like sugar of fat into simple substance like CO₂ & water.

External respiration or breathing:-

For the active tissue respiration, fresh air from outside is constantly taken in & the stale air given out by the lungs in the process of breathing. This process is naturally carried out in two stages : (a) inspiration or inhalation & (b) expiration or exhalation.

Mechanism of respiration:-To understand how breathing is effected, the following features of the respiratory apparatus must be noted :

(1)The walls & the floor of the chest cavity are muscular & therefore mobile.

(2)The pleural cavity are completely closed air can neither enter nor leave them.

Inspiration:-The inspiration or intake of air occurs when the chest cavity is increased in size. The enlargement of the chest cavity involve in following step –

(1)The external intercostals muscles between the ribs constrict this ribs the forwards & upwards.

(2)The muscles of the dome shaped diaphragm contract. This flattens the diaphragm, thus increasing the length of the chest cavity.

Expiration:-Expelling the air from the lungs or expiration takes place when the chest cavity is again reduced in size.

(1)The internal intercostals muscles contract so as to relax the external intercostals muscles. This pulls the ribs downwards & backward. The sternum is brought to its original position.

(2)The muscles of the abdominal wall press the abdominal viscera a gains the posterior surface of the diaphragm. This helps to restore its normal dome-shaped position.

Circulatory system:-

The vascular system is the transport system of the body. The nutritive substance is absorbed in the digestive tract pass into the circulatory fluids that serve as media for transport. These fluids are the blood & lymph.

The vascular system has four main components :– (1)A circulating medium, the blood

(2)Blood vessels like arteries capillaries and veins

(3) the pumping organ, the heart and

(4) the lymph and lymphatic system.

1)Blood :-

Blood is a complex fluid connective tissue. It is somewhat sticky, little heavier than water & slightly alkaline, reddish fluid. The specific gravity of the blood of rat is 1.056 & PH 7.35 – 7.45. The blood consist of a fluid plasma in which various types of cells, the blood corpuscles are suspended.

The plasma :-

The blood plasma is yellowish in colour & consists of 90-92 per cent water with various substances dissolved in it. Some of these substance are merely being transported while others form a part of the plasma itself.

a)Blood Proteins:- These include serum. Albumin, serum global in & fibrinogen. These are in a colloidal form & are responsible to make the blood viscous. The albumin & fibrinogen are however derived from the liver.

b)Organic Substance:- These include the nutrients & wastes. Many nutrients are usually present in the blood, these ported to the tissue. They include amino-acids, glucose & fats.

c)Salts:- Total amount of salts present in the plasma, form about 1% by weight. Chlorides, carbonates & phosphates of sodium, potassium & iron are the salts present in the plasma.

d)Hormones & enzymes:- Many substance are present in the plasma whose presence cannot be detected by analysis.

e)Gases:- Little oxygen is also dissolved in plasm, though it is mainly carried by the red corpuscles. Carbon dioxide is mainly transported by the plasma.

2)Red blood corpuscles (erythrocytes) :-

The red corpuses in rat, as in most of the mammals, are biconcave circular discs. Each corpuscle is bounded by a thin elastic envelope probably of a lipoid nature. It contains a spongy cytoplasm called stroma. A respiratory pigment, hemoglobin, is dissolved in this cytoplasm.

This gives a yellowish tint to the corpuscle however, when the corpuscles are seen in bulk, the colour appears to be rat. It has an affinity for oxygen, when blood circulates through lungs, it takes up oxygen & becomes oxyhemoglobin. Oxygen is held in loose combination with hemoglobin when the blood in circulation reaches the tissues, the red cells part with their oxygen & the blood becomes purplish in colour the red blood corpuscles of rat are about 9 – 9.5 million in number per cu.mm. of blood. The average size of the corpuscle is 6.3 in diameter. The number of R.B.C. is rather more in female than in the male rat.

3)The leucocytes (white blood corpuscles) :-

These are the nucleated and irregularly shaped blood cells. These lack the coloring matter & are hence called as the white corpuscles. They are often classified according to the form of the nucleus the nature & staining reactions of the cytoplasm.

The white cells are of two main types –

1. Lymphocytes or non-granular leucocytes &
2. Granulocytes.

I)The Lymphocytes :-

(1)The Lymphocytes have a large & single nucleus & non-granular cytoplasm, naturally the cytoplasm forms a small proportion as compared to the nucleus.

(2)Most of them are not capable of clear amoeboid movement.

(3)They constitute about 76% of the total number of white cells.

(4)They are small cells with bean shaped nuclei. In rat they form 1% of the total count of leucocytes.

II)Granulocytes :-

They are also known as polymorphonuclear leucocytes. They have a lobed nucleus. They are produced in bone marrow.

4)Blood platelets or thrombocytes :-

(1)The blood platelets are small rounded bodies. These are biconvex & without nuclei. These are said to be connected with clotting of blood.

(2)When exposed they soon break up into still more minute fragments; the latter clump together & liberate a substance called platelet factor.

(3)This substance really plays an important part in the clotting of blood.

(4)They are formed by the break-down of large cells in the bone marrow called megakaryocytes.

Function of blood :-

Transport :-

1)The blood conveys nutrient materials from alimentary canal to all the different parts in the body where they can be utilized to stored.

2)It takes up oxygen with the help of hemoglobin while passing through the capillaries in the respiratory organs and supplies it to all the tissues & cells in body for carrying out tissue respiration.

3)In return the blood carries away the waste of metabolism form all parts of the body to the organs from where they can be eliminated thus CO₂ & a little water are carried to the lungs are nitrogenous wastes like urea to kidneys.

4)The blood distributes heat which is set free by the chemical changes where there is much activity as in muscles & glands to the less active part.

5)The dustless glands in the body secrete very powerful agents known as chemical messengers or hormones; these act as stimulating or inhibiting agents to the actions or other organs.

(6)Protection:-The blood serves as an extremely important defense against the attacks of bacteria & other micro-organisms; this function is carried out by the leucocytes.

i)Some of them:- Phagocytes – flow round & engulf into their protoplasm, the harmful bacteria & parasitic micro-organisms & destroy them

ii)Some lymphocytes secrete substance called antibodies & antitoxins the antibodies act against germs & kill them. The antitoxins neutralize the toxins or poisonous substance produced by bacteria & disease germs.

7)With the help of fibrin in the plasma the clotting of blood is brought about. This prevents excessive bleeding from wounds. This also seals the wound against the entry of germs.

Arterial System Of Rat :-

Two major arterial trunks originate from the heart :-

1. The aortic arch or systemic aorta and
2. The pulmonary trunk.

The systemic aorta arises from the left the ventral & carries oxygenated blood to all part of the body except the lungs; while the pulmonary trunk arises from the right ventricles; it carries deoxygenated blood to the lungs. The bases of the two trunks appear to be twisted.

A) The systemic aorta :- It arises as a major trunk from the base of the left ventricles. It runs forwards & soon curves to the left. It bends round the bronchus forming the arch of the aorta from this arch arise three main arteries these are the (1) Innominate (2) Left common carotid and (3) The left subclavian.

1) Innominate :- It arises on the right side of the arch. It is also known as the brachia-cephalic artery shortly after its origin it divides into (a) a common right carotid & a right subclavian artery.

a) Right common carotid :- Arising from the innominate this artery lies parallel to the trachea & passes towards the head. Near the thyroid gland it divides to form the internal & external carotid arteries.

b) The right subclavian :- It arises from the innominate passes outwards between the first rib & clavicle. Three branches arises from the subclavian.

i)Right cervical arises anteriority; it lies parallel with external jugular vein & supplies the muscles in the neck region.

ii)Right internal mammary arises from the posterior face of the subclavian & supplies blood to the sternal region.

iii)Right costo – cervical arises very near the internal mammary & supplies the neck & upper part of the thoracic wall.

Dorsal aorta :-

The aortic arch while curving on the left gradually sinks to the dorsal side in the thoracic cavity it lies in the mediastinal space.

The dorsal aorta then perforates the diaphragm continues into the abdominal cavity till in iliac region it bifurcates to form two common iliacs.

A little posterior to the diaphragm, the dorsal aorta gives rise to two large unpaired visceral arteries, the (i) coeliac & (ii) anterior mesenteric.

B)Pulmonary trunk :- It originates from the base of the right ventricles, very near the origin of the aortic. It curves towards the dorsal side of the heart & then bifurcates into right & left pulmonary arteries.

Venous System Of Rat :-

Veins carry blood towards the heart. In rat there are three seats of veins : (A) systemic veins (B) pulmonary veins and (C) hepatic portal vein. The systemic veins carry deoxygenated blood whereas the pulmonary veins carry oxygenated blood. The portal system carries blood from the alimentary canal-spleen & pancreas to the liver.

A)Systemic veins :-

There are three systemic veins.

(a)Two precaval right & left.(b)A postcaval.

(c) Precaval – Each precaval vein) is formed by the union of jugular & subclavian vein.

1) The right precaval is formed by the union of the internal jugular & subclavian veins. It receives blood from the following veins.

2) The external jugular is a large vein it is principal vein of the neck in rat.

3) A cephalic vein from the shoulder region joins the external jugular.

4) A brachial from the arm & A subscapular from the shoulder region joins to form the axillary.

6) The internal jugular collects the blood from the deeper parts of the head & brain. It enters the precaval with the subclavian.

B) The postcaval vein or the inferior vena cava carries blood to the heart from the posterior region. It recessive following veins.

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1) A pair of common iliac veins join together to form the median postcaval vein.

2) A caudal vein draining the tail joins the postcaval at its formation.

Each common iliac is formed by the union of the internal & external iliac veins.

i) The internal iliac or hypogastric vein is formed by the union of the vesical veins from the bladder & other smaller veins darning parts from the pelvic region.

ii) The external iliac is formed by the union of the femoral and epigastric veins.

3) A pair of ilia – lumbar veins bring the blood from the lumbar region.

a) The hepatic portal system :- The vessels comprising this system receive blood from the different parts of the alimentary canal & the associated parts.

b) Pulmonary veins :- The oxygenated blood from the right and left lungs is collected by the respective pulmonary veins. A single vein brings the blood from the left lung.

The Heart of Rat :- External Structure of Heart.

HEART VENTRAL

HEART DORSAL

• The heart lies in the ventral part of the thorax between the two lungs.
• It lies in the pericardial cavity enclosed by a double-layered membranous bag, the visceral pericardium immediately invests the heart.
• The outer or the parietal layer forms the wall of the pericardial cavity.
• The space between the two layers is filled up by a shock absorbing lubricating fluid called the pericardial fluid.
• The heart is an ovoid part consisting of four chambers; two atria (auricles) and two ventricles.
• The greater portion of the heart consists of two ventricles; these together form a thick-walled cone with a broad anterior base 1 a pointed posterior apex an oblique groove separates the two ventricles.

• The groove extends from the right side of the base to the left side of the apex the groove contains the branches of the coronary artery & vein which ramify over the surface of the ventricle the left ventricle is much larger than right one in front of each ventricle is a much smaller chamber, the auricle.
• Each auricle in a contracted state presents a lobe, the auricular appendage, that projects over the ventricle.
• Between the two auricles lies a large pulmonary artery it originates from the right ventricles & soon curves to the dorsal & left side : it then bifurcates into the right & left pulmonary arteries.
• The veins open into the heart on its dorsal side.
• The three systemic veins viz. the two precaval & the post-cavil vein, open directly into the right auricle.
• The two pulmonary veins join together & open into the left auricle by a common opening.

Internal structure of the heart :-

1) The cavities of the two auricles are separate from one another by the inter-auricular septum.

2) The right auricle receives the deoxygenated blood from the systemic veins.

3) It has three separate apertures for the respective venae guarded values.

4) A membranous fold the Eustachian valve, extends from the postcaval vein forwards towards the auricular septum.

5) From inner surface of the auricle numerous cords of muscle fibers arise; they are known as muscular pectinate.

6) The opening is guarded by a large tricuspid valve, composed of three triangular membranous flaps or cusps.

7) The left auricle receives oxygenated blood from the lungs. There is a single opening of the common pulmonary vein in its dorsal wall the left auricle opens into the left ventricle.

8) This left auriculo ventricular aperture is guarded by a bicuspid or mitral valve, consisting of two membranous cusps with cordage tendinea & muscular papillates.

9) The ventricles are very thick-walled & muscular.

10. The wall of the left ventricle is much thicker than that of the right.
11. This is in keeping with the fact that the right ventricle has to force the blood into the lungs in close vicinity.

11) The walls of ventricles shows bundles of muscle fibers arranged to form longitudinal ridges, the columnar carnie.

12) These are more strongly developed in the ventricle.

13) The right ventricle gives off, at its left anterior angle a large pulmonary aorta.

14) The opening of the ventricles to the aortae, both systemic & pulmonary are guarded by sets of three semi-Lunar valves.

Working of Heart :-

1)The walls of the heart are composed of special type of muscle called the cardiac muscle.

2. Their actions are involuntary, automatic (self regulating) & rhythmic.
3. They are peculiar to the heart only; they are not found elsewhere in the body.

4) These muscles maintain a life-long Rhythmic contraction with the necessary regularity.

4)The rhythm may change according to necessity becoming faster when the animal is very active or going slow whenever it is resting.

5)The rate of this rhythm is affected by impulses from the parasympathetic fibers of the cardiac branch of the vague nerve as well as the sympathetic fiber of the cardiac nerves.

6)The parasympathetic impulses slow the heart down, while the sympathetic impulses. Stimulate it & make it & the beat more rapid.

7)The throbbing of the heart is initiated & regulated by two bundles of special muscle fibers in the wall of the heart.

8)The one that initiates the rhythmic beat is embedded in the wall of the right auricle very close to the opening of the three cavil veins. It is called the Sino-auricular node.

9. The one of that regulates the heart beat is situated at the auriculo-ventricular junction.
10. This is known as the auriculo-ventricular node or the ‘bundle of His’.

10) The right auricle receive the deoxygenated blood through the venae cave & the let one receives the oxygenated blood from the lungs.

11. The flow of blood in the auricles stimulates the sinus auricular node.
12. It sends a wave of contraction along the walls of the auricles.

12) In the wall composed of cardiac muscle, the wave of contraction passes in a wave like manner from fiber to fiber.

13. This relays the movement started in the auricles to the apex of the ventricles.
14. The contraction of the ventricles follows slightly after that of the auricles.
15. This contraction of the ventricles is known as the systole.

14) The venous blood from the right ventricles is forced into the pulmonary aorta & the oxygenated blood of the left ventricles into the caroticosystemic arch or the aorta.

15) The flow of blood into the auricles is prevented by the tricuspid & bicuspid valves.

16) After a little pause which is known as the period of diastole the ventricles relax.

17) At this time the backward flow of blood from the pulmonary & systemic aortae into the respective ventricles is prevented by the presence of semilunar valves at the entrance of these aortae.

18) The two auricles & the two ventricles contract & relax alternately burring these movement, the heart is never empty.

19. The powerful contractions of the ventricles from the cardiac cycle or the heart beat.
20. It consist of period of systole (contraction) & a period of diastole (relaxation & rest).
21. The heart or rat beats approximately 300 times a minute whereas the human hearts beats about 72 times a minute.
22. This rate is of heart beat is controlled by the cardiac branches of the vague nerve.

21) Peculiarities of the mammalian heart and the associated arterial arches.

22) The development of a four-chambered heart, reduction of the sinus venosus to a small region like the Eustachian valve incorporated in the wall of the right auricle, & the division of the conus arteriosus to form two distinct trunks – pulmonary & the aortic – are the chief points.

23. The division of the regions – auricular & ventricular with the help of the inter-auricular & inter ventricular septa divides the heart completely into two halves.
24. The right half contains the deoxygenated blood & the left half, the oxygenated one there is no mixing of the two types of blood.
25. This has established a complete double circulation.

24) The aortic arches also are modified the arches 1, 2 & 5 have completely vanished.

25) The right side of the arch is represented by the proximal part of the right subclavian artery.

Double circulation :-

The circulation in rat or mammals in general can be summarized as follows :

1) The oxygenated blood from the left ventricles passes to all parts of body through the aorta & its branches.

2. In the tissues of the different parts of the blood flows through the capillaries.
3. Where exchange of materials takes place & the blood becomes impure-deoxygenated.
3. It is brought back by the cavil veins to the right auricle.
4. This is often called as systemic (body) circulation.

4) Right auricle the blood passes through the right ventricles and the pulmonary arteries to the lungs.

5) In the substance of the lungs when the blood is flowing through the capillaries it is oxygenated.

6)This pure blood returns to the left auricle of the heart through the pulmonary veins, this is pulmonary circulation.

7)Lymphatic system :- Closely associated with the blood vascular system is the lymphatic system. It consist of lymph sinuses (spaces), vessels, nodes (glands) & lymphatic ducts.

8)Lymph :- Lymph is a colorless fluid, similar in composition to the blood except that then it has no red corpuscles. It is actually derived from the blood when the latter flows. Through the capillaries in the living tissue. It is also known as tissue fluid. It is important role of actual supply of food & oxygen to the tissue cells.

9)Lymph sinuses are widely distributed throughout the body. Large space occurs between the integument & muscles, muscles & bones etc.

10) Lymph vessel possess valves. They unite in turn to form lymphatic ducts or trunks. These trunks eventally empty into large veins.

11) The largest lymphatic duct, the thoracic duct, lies to the left of the spinal cord.

12) It extends anteriorly from the renal region near the first rib it opens into the venous system.

13) Spleen :- The spleen constitutes the largest mass of the lymphoid tissue in fact it should be considered a part of the lymphatic system.

iv) Nervous System of Rat :-

Thus the nervous system can be conveniently system divided under the following three heads :-

1) Central or cerebra-spinal nervous system consisting of the brain & the spinal cord.

2) The peripheral nervous system consisting of the cranial nerves originating from the brain and spinal nerves from the spinal cord.

3. The autonomous nervous system that controls the in voluntary activity.
4. It consists of the parasympathetic system and the sympathetic system.

1)The cerebra-spinal nervous system :-

• The brain & the spinal cord together from the central N.S. as in all other vertebrates, the medullary plate of the embryo becomes rolled up into a neural or nerve tube.

• It gets differentiated into an enlarged anterior part forming the brain.
• The posterior part of the tube becomes the spinal cord.
• The brain lies within & protected by the cranium (skull) while the spinal cord is protected by the vertebral column.

Meninges :-

1) The brain & spinal cord are completely unsheathed by three layers of membranes called meninges.

2) The outermost is the tough dura mater; it lines the cranium & the vertebral canal.

3) The middle layer is the arachnoid mater.

4) It is rather delicate; it is separated from the dura mater by the subdural space.

5) It is also separated by the inner layer the sub-arachnoid space.

6) The inner most of the meninges in the pia mater.

7) It is more or less nutritive layer.

8) The sub-Dural & sub-arachnoid space are filled with a lymph-like cerebra-spinal fluid.

9) This fluid acts as a lubricant and shock absorber.

10) It thus help to protect the delicate nervous tissue from mechanical injuries.

11) In amphibians, reptiles and birds only two membranes, the dura mater and pia mater are present.

12. The pia mater in mammals however, gets differentiated into the mechanoid and piamater.
13. This in mammals three covering are present as mentioned above.

The brain lies within & protected by the cranium. The cranial N.S. arising from the brain emerge through a number of foramina in the skull. The brain is divided into three regions; the fore brain, mid-brain & hind brain the latter becomes continuous with the spinal cord.

Fore brain :- The fore brain or prosencephalon is subdivided into anterior telencephalon and posterior thalmencephalon.

Telencephalon :-

1) The telencephalon mainly consist of the olfactory lobes & the large cerebral hemispheres.

2) The telencephalon forms many parts in the brain.

3) Anteriorly it forms the olfactory lobes, olfactory tracts & hippocampi.

4) It posteroventral part forms the corpora striata; while its dorsal part forms the pallium.

5. The olfactory lobes constitute the most anterior part of the telencephalon.
6. They are relatively small.

6) The project a little Infront of the cerebrum.

7) The latter are the association centers for the sense of smell.

8)The olfactory regions are demarcated from the cerebral hemispheres by the longitudinal grooves called the rhinal fissures.

9)The olfactory lobes & the hippocampal lobes are often said to constitute the rhinencephalon.

10) The pallium in the higher vertebrates has an increasing number of nervous cells forming the cerebral cortex.

11. It consist of two large cerebral hemisphere.
12. They from the anterior 2/3 part of the brain.

Thalmencephalon :-

The thalmencephalon is also called as diencephalon (twin-brain or twixt brain) it lies between the telencephalon & mesencephalon. It contains a cavity, the third ventricle. It is completely masked in dorsal view by the over hanging cerebral hemispheres. Three regions are distinguished in the diencephalon.

a)The small dorsal epithalamus.

b)The ventral hypothalamus.

c)The lateral walls forming the thalami.

Mesencephalon :-

• The mid-brain or mesencephalon undergoes the least modification during its development it is thick walled region connecting the fore-brain & the hind-brain.
• It is cavity is a narrow canal called iter, it connects the third ventricles with the fourth ventricle.
• The mesencephalon forms optic lobes dorsally & crura cerebri ventrally.
• The larger two posterior lobes are the inferior colliculi.
• They contain centers for auditory impulses.
• They optic connect the thalami of the fore brain & with the hind-brain & spinal cord.

Rhombencephalon :-

The hind brain is the rhombencephalon. Its anterior part gives rise dorsally to an elevated surface, the metencephalon. The rest of its dorsal part of & the ventral part form the myelencephalon.

Metencephalon :-

The dorsal part of the metencephalon gives rise to the cerebellum. It is greatly thickened & well developed region. It projects forwards until it meets the posterior margin of the cerebrum; it also extends laterally. It median lobe is called the vermis; its lateral extensions are called floccule and parafollicular. The white matter forms a characteristic dendritic (tree-like) pattern called arbor vitae. This can be well seen in a longitudinal section of the cerebellum.

Immediately behind the hypophysis is a heavy, fibrous band, the pons virally. It is a characteristic of the mammalian brain. It connects the two sides of the cerebellum.

It also contains relay centers from the cerebral cortex to the cerebellum. Below the cerebellum the metencephalon contains the anterior portion of the third ventricle by an aqueduct of Silvius.

Myelencephalon :-

This region on the ventral side forms the medulla oblongata it form the greatly thickened. Lateral and ventral wall of the fourth ventricle contained internally the thin roof of the ventricle is highly vascular. Together with the overlying pia mater it forms the posterior choroid plexus. The forth ventricle extends posteriorly narrows down & become continuous with the central canal of the spinal cord. The medulla ablongeta is the posterior most part of the brain. It becomes continuous with the spinal cord. In fact it appears like an enlarged part of the spinal cord & Bence is sometime called as the spinal bulb. The medulla oblongata contains the centers that govern the involuntary activities such as the rate of heart beat, respiration swallowing vomiting etc.

Function of brain :-

Fore-brain :-

1)Olfactory lobes are concerned with the sense of smell.

2)The hippo carpal lobes act as the association centers for the sense of smell.

3)The cerebral hemispheres are the center of coordination and intelligence the neopallium or the cerebral cortex is the seat of menu. y, will, intelligence & all conscious sensations & actions.

4)The corpus callosum adds to the efficiency of the coordination of the two sides of the hemispheres.

5)The pineal and pituitary bodies have endocrine functions.

6)The optic thalami act as association centers for the banes of sight. They also act as centers where all the sensory impulses are relayed before transmitting them to the cerebral cortex.

7)The anterior choroid plexus forms the cerbro-spinal fluid.

Mid-brain :-

In the corpora quadrigemina, the anterior pair of lobes is concerned with the sense of sight; while the posterior pair of lobes is concerned with the relay of auditory sensation.

Hind-brain :-

1) The cerebellum controls the muscular activity and maintains the posture. It is concerned with the sense of balance & equilibrium.

2) The pons variola contains the relay centers that transmit impulses from the cerebral cortex to the cerebellum.

3) The medulla oblongata controls the involuntary activities such as the heart beat breathing, swallowing etc.

4) The posterior choroid plexus, like the anterior one, is concerned with the formation of the cerebra-spinal fluid.

The Spinal Cord Of Rat :-

T.S. of Spinal Cord

1)The spinal cord in rat as in all vertebrates lies in the neural canal i.e. the canal formed by the neural arches of the vertebrae like the brain it is covered over by the meanings.

2)The cerebra spinal fluid fills the spaces between these protective membranes and also lies around them.

3)It is roughly cylindrical but slightly flattened darso-ventrally.

4)It is marked by two deep longitudinal grooves, the dorsal & ventral fissures.

5)The diameter of the spinal cord is almost uniform except for two slight enlargement one in the cervical region at the base of the neck & another in the lumber region.

6)From the cervical enlargement arises the nerves supplying the fore-limbs, while the nerves to the hind limbs arise from the lumbar enlargement.

7)Posteriorly, behind the lumbar enlargement, the cord abruptly narrows to a fine thread the filum terminal.

8)In rat the filum terminal starts from the second lumbar vertebra & extends into the tail for a short distance.

9)Internally, the spinal cord is hollow; it is traversed by a narrow central canal, which anteriorly becomes continuous with the fourth ventricle of the brain.

10)The spinal cord is composed of the central grey matter surrounded by the while matter.

11)The grey matter consists mainly of the neuron cell bodies and is arranged roughly in H-shaped pattern. It shows two pains of horns, dorsal & ventral horns.

12)The surrounding white matter consists mainly of the tracts of medullated nerve fibers.

Peripheral nervous system :-

The peripheral nervous system comprises the cranial nerves originating from the brain and the spinal nerves from the spinal cord.

a) Spinal nerves :-

(1) These are paired nerves arising from the spinal cord. Each spinal nerve has two roots; the dorsal root &the ventral root. (2) The ventral root has only motor fibers whose cell bodies are situated in the spinal cord. (3) The two roots join together before the spinal nerve emerges out though the inter. Vertebral notices. Each nerve soon after its formation divides into a small dorsal ramus to the skin & muscles of the back & the main ventral & ramus supplying the ventral & lateral parts. The rat has 34 pairs of spinal nerves 7 cervical, 13 thoracic, 6 lumbar, 4 sacral & 3 caudal at the level of the fore-limbs a conspicuous brachial plexus is formed. It is composed of the ventral rami of 4^th to 8^th cervical and the

first thoracic spinal nerves. The lumbo-sacral plexus is formed from seven nerves, 1 to 6 lumbar and the 1^st sacral nerve. This supplies the hip region & the hind limbs. A small prudential plexus can be marked posteriorly on either side. It consists of branches from 7 nerves, 6^th lumbar 1.4 sacral & 1-2 caudal. It serves the anal region & the muscles of the tail many of the spinal nerves emerge considerably posterior to their points of origin in the spinal cord.

b) Cranial nerves :-

There are 12 pairs of cranial nerves in rat as in all mammals. They are designated by Roman numerals as well as names are as signeted to them. These nerves lack the regularity of occurrence characteristic of the spinal nerves.

Some of them are entirely sensory, some purely motor & the rest of a mixed type, including both sensory and motor fibers the name, origin, nature & distribution of these nerves is given below in a lobular form.

Autonomic Nervous System :-

This system is sometimes called as the visceral nervous system. It is a special division of the peripheral nervous system that controls involuntary activity. It is concerned with the activities of the visceral ports like the intestine. Blood vessels, heart, bladder & reproductive organs, most of these organs recessive a double set of nerves from the autonomic nervous system one set stimulates the activity & the other set inhibits the activity. The ganglia are connected with the brain & spinal cord on the one head & the parts to be supplied on the other. The fibers going from the autonomic system to the organ to be innervated are called the post ganglionic fibers; these are non-medullated.

A)Sympathetic System :-

In the sympathetic system, the preganglionic fibers are relatively shorter than the postganglionic fibers.

The system consist of a double chain of ganglia joined together by sympathetic cords, one on either side of the vertebral column. Rat shows 24 pairs of sympathetic ganglia : 3 cervical, 10 thoracic, 6 lumbar, 4 sacral & 1 caudal. In rat a large celiac or solar plexus lies near the root of the celiac & anterior mesenteric arteries.

B) Parasympathetic System :-

It is made up of cranial and sacral autonomic ganglia. Their preganglionic fibers are relatively long in the cranial region the fibers arise from the third, seventh, ninth & tenth cranial nerves in the sacral region, the preganglionic fibers arises from some of the sacral nerves. These autonomic fibers go to the eye, salivary gland heart, bronchi stomach, intestine, liver pancreas, kidney etc. the parasympathetic ganglia lie in the organs served by them. The two systems are antagonistic in their actions. Lie they work opposite to each other if the sympathetic fibers accelerate any activity the parasympathetic would regard the same.

For examples :-

The parasympathetic system increases the secretions of glands whereas the sympathetic system decreases the secretions.

Eye of Rat :-

1)The rat’s eye has the same basic strut. and function of all mammalian eyes, including the human eye.

2)These structure focus the light on the retina, a layer of light receptors at the back of the eye.

3)These receptors translate the image into a neural message which travels to the brain via the optic nerve.

4)Light passes through a layer of transparent tissue at the front of the eye, called the cornea.

5)The cornea bends the light & is the first element in the eye’s focusing system.

6)The light then passes through the anterior chamber, a fluid filled space just behind the cornea.

7)This fluid is called the aqueous humor, & it is produced by a gland called the ciliary body.

8)The light then passes through the pupil a round opening in the center of the iris.

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9. The iris is a ring of pigmented.
10. Muscular tissue that controls the size of the pupil, which regulates how much light enters the eye the pupil grows large in dim light & shrinks to a small hole in bright light.

11) The light passes through the lens, a transparent, biconvex body that helps focus the light from the lens passes through the vitreous body, a clear jelly – like substance that fills the back part of the eye ball, & is focused onto the retina a layer of light – sensitive tissue at the back of the eye.

12) The retina contains light sensitive cells called photoreceptors, which translate the light energy into electrical signals.

Ear of Rat :-

1)The rat is of value in ontological research for many reasons for instance, the middle ear strut. are easily approachable. Recently a couple of studies in the rat have been published concerning the healing pattern of tympanic membrane perforations & mucosal changes following Eustachian tube blockade including the otitis media with effusion.

2)The middle ear cavity of the rat is lined with ciliated & squamous epithelium.

3)The arrangement of the ciliated cells, in distinct tracts and their continuity with the ciliated epithelium of the Eustachian tube, suggests the existence of a conciliary transport system for cleaning the middle ear cleft.

4)The secretory cells produce either neutral or sulphated glycoproteins, dependent on their location.

5)In addition to these secretions, the Eustachian tube is bathed with secretory products of seromucous glands.

6)Also in the areas with squamous epithelium, numerous small secretory cells, the character of which is only identifiable with the electron micro scope, are present.

7)It is concluded that the middle ear lining can be considered as a locally modified respiratory epithelium.

8)The Blockade of the conciliary transport system, supposedly a crucial etiological factor in secretory otitis media, by obstruction of the Eustachian tube, induces pathogenic behaviors of microorganisms normally present in the middle ear.

9) This results in either a transient or a longstanding infective middle ear disease, associated with a large variety of changes of the mucosa, especially with respect to the secretory activity.

10) The data obtained indicate that the increased secretory activity encountered in secretory otitis media can not be attributed to the isolate effect of tubal occlusion, but rather to an infective process.