STERNUM OF RABBIT

Written by Sunday, 02 July 2017 15:31
In the mid ventral region of thorax of Rabbit sternum is present. It is made by five bony pieces called "Sternabrae". It is called "mesosternum". This will show "presternum" anteriorly. It is a long bony piece. It is connect­ed with clavicles. On the lower side mesosternum it articulates with xiphi-sternum, which ends with xiphoid cartilage.

The ribs articulated with sternum by their cartilage part. In rabbit the first pair of ribs are attached to the presternum.

Uses of sternum :Thus sternum gives strength and support to the body on the ventral side. It helps in the process of respiration also.

ORGAN OF CORTI OR COCHLEA

Written by Sunday, 02 July 2017 08:08
The internal ear of rabbit includes "organ of corti" or Cochlea spirally coiled. Lagena is enclosed and fused with the spirally coiled j the preotic bone which form cochlea. Cochlea is a bony tube line connective tissue. The cavity of the cochlea is transverse by two brines. It is divided into 3 cavities. They are
 
  1. Scala vestibuli
  2. Media
  3. Scala tympani.

The middle cavity is filled with endo lymph membranes that cover the Cochlea are Reisner's membrane and membrane. The epithelium of basilar membrane is highly modified. It is "organ of corti". It has hair cells and supporting cells. It is supported by cochlear branch of 8th cranial nerve. It is useful for hearing.
 
  1. Posterior semi circular canal
  2. External semi circular canal
  3. Anterior semi circular canal
  4. Ampullae
  5. Utriculus
  6. Sacculus
  7. Ligament.
  8. Cochlear duct

CLASSIFICATION OF MAMMALS: THERIA

Written by Sunday, 02 July 2017 01:19
THERIA
 
This group includes Mammals which show true mammals characters

Infraclass Metatheria:
 
They show almost all the Mammalian characters.
 
  1. Females show brood pouch or Marsupium on their ventral abdomen.
  2. Sebaceous glands are modified into mammary glands.
  3. Pelvic girdle shows epipubic bones. This supports Marsupium.
  4. Ribs are two headed.
  5. Carpus callosum is absent.
  6. Vagina and uterus are double (didefphic condition)
  7. They give birth to immature young ones.
  8. This infra class includes 1 order.
 
Order Marsupialia:
 
Ex: a) Didelphis – Opossum, b) Dasyurus - Tiger cat, c) Paramales - Bandicoot, d) Macropus - Kangaroo, e) Notorgetes - Marsupial mole
 
Infraclass Eutheria:
 
  1. Mammary glands are well developed.
  2. Double headed ribs are seen.
  3. Carpus callosum is present.
  4. Urinogenital organs will open independently into the Rectum.
  5. Testis are extra abdominal.
  6. Uterus and vagina are single.
  7. They show placenta in the development of embryo. This infra class is divided into following orders.
 
1. Order: Insectivora:
 
  1. Small animals are seen in this order.
  2. Snout is long.
  3. Five toed feet are seen.
  4. They are Nocturnal and Terrestrial
 
Ex: 1) Paraechinus (Hedgehog), 2) Talpa (mole), 3) Echinosorex (Shrews)
 
2. Order: Dermopetera:
 
  1. In between fore limbs and hind limbs, in between head and fore limb, in between hind limbs and tail, membrane is formed. This helps for gliding in air.
  2. They are Nocturnal.
 
Ex: Galeopithecus (Flying lemur)
 
3. Order: Chiroptera:
 
  1. Fore limbs are modified wings.
  2. Hind limbs are weak.
  3. Digits are clawed.
  4. Eyes are small and vision is very weak.
  5. They are usually called Bats.
 
Ex: Pteropus (Flying fox), Megaderma (Vampire bat)
 
4. Order: Primates:
 
  1. Hands and feet are more or less prehensile.
  2. Thumb is oppossable to other digits.
  3. Only two pectoral mammary glands are present.
  4. Cerebrum is big and convoluted.
 
Ex: 1) Chyromys (Aye aye), 2) Loris, 3) Hylobates (Gibbon), 4) Anthropithecus (Chimpanzee), 5) Simia satyrus (Orangutan), 6) Macaca (Monkey), 7) Homo Sapiens (man)
 
5. Order: Edentata:
 
  1. Feet has 5 digits. They are clawed.
  2. Testis are abdominal.
 
Ex: 1) Dasypus = ormadilla, 2) Bradypus = Three toed sloth, 3) Myrmecophaga' = Giant ant eater
 
6. Order: Pholidota:
 
  1. The body is covered by scales.
  2. In between scales hairs are present.
  3. Teeth are completely absent.
  4. Tongue is long, sticky and protrusible (Helpful to catch the ants).
 
Ex: 1) Manis (scaly ant eater or parigolin)
 
7. Order: Lagomorpha:
 
  1. Small mammals
  2. Tail is short.
 
Ex: Oryctologus - Rabbit, Lepus (Hare)
 
8. Order: Rodentia:
 
  1. Small mammals.
  2. Canines are absent. (Diastema is present)
 
Ex: Ratus ratus - Rat, Funambulus - Squirrel, Hystrix - Porcupine.
 
9. Order: Cetecea:
 
  1. Large aquatic animals.
  2. Body is spindle shaped and fish like.
  3. Hair is absent.
  4. Neck is absent.
  5. Fore limbs are modified into paddles.
  6. Hind limbs are absent.
 
Ex: Orcinus - Killer whale, Physeter - Sperm whale (Largest toothed whale) Plantanista – Dolphin
 
10. Order: Sirenia:
 
  1. These are all aquatic mammals. They are called sea - cows.
  2. Hind limbs are absent.
  3. Testis are abdominal.
 
Ex: Halicore dugong (dugong- sea cow), Trichecus (Manatee)
 
11. Order: Carnivora:
 
  1. They are terrestrial, arborial or aquatic mammals.
  2. Mammary glands are present on abdomen.
  3. The last premolar is called carnassial teeth.
 
Ex: 1) Panthera leo - Lion, 2) Pathera tigris - Tiger, 3) Acinomyx - Leopard, 4) Vulpes - Fox, 5) Trichecus - Walrus.
 
12. Order: Tubulidentate:
 
  1. Body is stout and pig like.
  2. Skin is covered by thick and less hair.
  3. Ears are long, errect and pointed.
 
Ex: Orycteropus
 
13. Order: Proboecide:
 
  1. Largest Terrestrial Mammals.
  2. Long probosis is seen.
  3. Incissors will become Tusks.
 
Ex: 1) Elephas - Indian elephant
 
14. Order: Hyrocoidea:
 
  1. Small Rabbit like
  2. Ears arc short
 
Ex: Procavis

15. Order: Perissodactyla:
 
  1. Single Looted mammal.
  2. The middle light of limbs will develop hoof.
 
Ex: 1) Equas (Horse), 2) Rhinoceros – Rhinoceros

16. Order: Artiodactyla:
 
  1. Terrestrial, semi aquatic animal.
  2. Limbs have two hooves.

Ex: Hippopotamus - Horse of River Camelus - Camel, Sus - Pig

CLASSIFICATION OF MAMMALS: PROTOTHERIA

Written by Sunday, 02 July 2017 01:06
Mammalia is divided into two subclasses. 1) Prototheria 2) Theria
 
GENERAL CHARECTERS OF PROTHERIA
 
  1. External pinnae are absent.
  2. In the young stage teeth are present and in the adults horny plates are formed.
  3. Mammary glands are present and tears are absent.
  4. Body is covered by hairs.
  5. Pelvic girdle shows epipubic bones.
  6. Vertebrae will not show epiphyses.
  7. Ribs are single headed. (Tuberculum is absent)
  8. Corpus callosum is absent in brain.
  9. Cochlea is simple and is not coiled.
  10. In the males the testis is abdominal.
  11. Females are egg laying. Hence prototherians are called egg laying Mammals.

This subclass includes only one order that is Monotremata.
 
Order Monotremata:
 
Thesemammals show prototherian char­acters. They can found in Australia, Tasmania and New-guinea.
 
Prototheria echidna thumb17

Ex: 1. Echidna (Spiny ant eater), 2. Ornithorhyncus (Duck billed platypus)

GENERAL CHARECTERS OF MAMMALS

Written by Saturday, 01 July 2017 23:57
Mammal like Reptiles therapsida might have given Mammals. It occured at the end of Triassic period of Mesozoic era. In Jurassic period only few mammals existed. In the coenozoic era these animals increased their number and became very complex. This era is called 'age of mam­mals'. Today nearly 8500 species of mammals are living in the world. Their body is covered by hairs. They show external ears called Pinnae. They are warm blooded organisms. They show mammary glands. They feed their young ones with milk.
 
GENERAL CHARACTERS OF MAMMALS

In the upper carboniferous period of palaeozoic era Mammal like reptiles are developed. From them early mammal like forms are developed. In the Jurassic period of mesozoic era few mammals are existed. In the coenozoic era different Mammals are developed. Hence this era is called as age of Mammals. The Mammals evolution radiated in many ways and occupied all parts of the globe.
 
  1. Mammals are warm blooded animals.
  2. The body is covered by hairs.
  3. 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.
  4. In Mammals mammary glands are present. They are functional in female. They are modified sebaceous glands. But in prototherians they are modified sweat glands.
  5. External ears are present (Pinnae). The middle ear contains 3 ear ossicles. They are malleus, incus and stapes. The internal ear contains highly coiled hearing organ called organ of Corti or Cochlea.
  6. External Nostrils open into the internal nostrils. They open into pharynx.
  7. Dentition in Mammals: The teeth are Heterodont. 4 types of dissimilar teeth are present. (Incissors, Canines,Premolars, molars.) The teeth are diphyodont. (Two sets of teeth are developed). Thecodont teeth are present in sockets of jaw bones.
  8. The skull has two occipital condyles. Hence it is called dicondylic skull.
  9. The lower jaw is made by single bone called dentary.
  10. The, vertebrae are Amphiplatyan type. Each vertebra is composed of one centrum and two epiphyses.
  11. In the neck of Mammals seven cervical vertebrae are present. In Sirenia has only 6 cervical vertebrae.
  12. The ribs are double headed, capitulum, Tuberculum.
  13. The fore and hind limbs bear digits which will not be more than five.
  14. The body cavity is divisible into two parts, It is because of the presence of a muscular diaphragm. The upper is thoracic cavity and lower abdominal cavity.
  15. Heart shows 4 chambers.
  16. Only left aortic arch is present.
  17. Non-nucleated R.B.C. is present.
  18. Brain is well developed.
  19. In brain 4 optic lobes are present. Cerebrum is well developed.
  20. Metanephric kidney is present.
  21. In the nephron Henley loop is present.
  22. Penis is present.
  23. Male and females are separate.
  24. They give birth to young ones. But in Monotrems they lay eggs.
  25. In the uterus the foetus grows. This period is called Gestation period. Foetus is nourished by placenta through placental connection.

PECTEN IN BIRDS

Written by Saturday, 01 July 2017 23:45
In the eye of the bird a comb like structure is present. It is called pecten. It is soft and vascular. It is a rectangular plate. It projects into the vitreous humour from the blind spot.
 
Functions of Pecten:
 
  1. It protects the retina from sunlight by casting shadow on it.
  2. Pecten gives additional nourishment to the retina.
  3. It exists pressure on the lens and alter its curvature for accommodation.

SYNSACRUM IN BIRDS

Written by Saturday, 01 July 2017 23:29
In the birds vertebral column compound structure is present. It is called Synsacrum. It is formed by the fusion of 14 to 16 vertebrae. Those vertebrae are one last thorasic vertebra, Six lumbar vertebrae, two sacral vertebrae and seven candal vertebrae. This structure supports llia of the pelvic girdle.

The lumbar vertebrae will show well developed transverse pro­cess. Their neural spines are fused to form a crest.

The centrum of the sacral vertebrae are fused together and their transverse processes are also united to form bony plates. It will give support to the llia.
 
The last part of the synsacrum is formed by the union of first seven caudal vertebrae. Thecentrum of these vertebrae are laterally compressed. Their transverse processes are divided into dorsal and ventral portions. The dorsal portions of these vertebrae will fuse to form bony plates. The ventral portion is rod like. It is considered as a rib.

All the vertebrae of Synsacrum are completely fused and it is difficult to identify them separately.

BODY WALL OF BIRDS (AVES)

Written by Saturday, 01 July 2017 19:50
The body wall of birds has three regions, Skin, Muscles and Perito­neum.
 
  1. The skin is dry. It shows upper stratum corneum, which has flat cornified cells. The feathers cover the body. Dermis shows musculo-fibrous tissue. The muscles help to raise and lower the feathers. It is supplied with blood vessels and nerve fibres.
  2. Glands are absent in the skin of a bird except preen gland which is located on the upper surface of the tail. Its secretions keep the feathers water proof.
  3. Muscles: Below the skin Muscles are present. In birds skeletal muscles are well developed. The flight muscles are well developed which help to raise and lower the wing.
  4. Peritoneum: A thin epithelium called peritoneum will cover the inner surface of the muscles.
  5. In birds skin sweat glands are absent and hence bird cools itself in hot environment by panting.

CLASSIFICATION OF AVES

Written by Saturday, 01 July 2017 17:28
Based on characters of  Aves Class is divided into 2 sub-classes.

Sub class: i) Archeornithes and Subclass ii) Neornithes
 
1. Sub class Archeornithes:
 
  1. In this subclass extinct birds are included. Those birds were alive in Mesozoic era.
  2. These show a long tail with 13 or more than 13 caudal vertebrae.
  3. Pygostyle is absent.
  4. Meta carpals are free. The free fingers of fore limb will end with claws.
  5. Thecodont teeth are seen.
 
Archeopteryxfossil thumb10
 
Eg: Archeopteryx, Archeormis
 
2. Sub class Neornithes:
 
  1. This subclass includes both extant and extinct birds.
  2. Tail ends in pygostyle. The rectrices are arranged r a semi circular around pygostyle.
  3. Teeth are absent in many forms.
  4. Sternum is well developed. It shows a keel to which flight muscles are attached.

This subclass is divided into 4 super orders.
 
  1. Odontognathae
  2. Palaeognathe
  3. Impennae
  4. Neognathae
 
1. Super Order: Palaeognathae:
 
  1. These are flightless birds.
  2. They are more in numbers.
  3. Wings are reduced or absent.
  4. Teeth are absent.
  5. Caudal vertebrae are free.

This super order is divisible into 7 orders.

1. Order: Struthioni:
 
Ex: Struthio camelus (Two toed African Ostrich (or) Ostrich)
 
  1. Large flight-less bird.
  2. Feathers are less.
  3. They show two toed hind limbs.
  4. Sternum is without keel.
  5. Neck is very long and flexible.
  6. Pygostyle is absent.
  7. These birds are good runners.
 
StruthioAfricanOstrich thumb10

2. Order: Rheiforms:
 
Rhea americana. (three toed (or) American ostrich).
 
  1. This includes flightless, terrestrial bird.
  2. They are good runners.
  3. Wings are better developed.
  4. The body shows more feathers.
  5. The hind limb bear three toes.
  6. Sternum is without keel.
 
Rheaamericanaostrich thumb15

3. Order: Casuariformes:
 
Ex: Casuarius (Casso waries), Dromaeus (Emu)
 
  1. These are flightless terrestrial birds.
  2. Head shows few feathers.
  3. Neck and body show more feathers.
  4. Wings are Rudimentus.
  5. The hind limb shows three toes.
 
Casuariusemu thumb11
 
4. Order: Aepyomithiformes:

Ex: Aepyornis.
 
  1. These are extinct elephant birds.
  2. Wings are vestigeal.
  3. Legs are powerful.
  4. Hind limbs show 4 toes.
  5. Sternum is broad.
  6. Keel is absent.
  7. Eggs are very big.
 
5. Order: Dinomithiformes:
 
Ex: Dinornis (Extinct Moas)
 
  1. These are gaint flightless extinct birds.
  2. Wings are absent.
  3. Eggs are massive.
  4. Sternum is reduced without keel.
  5. Pectoral girdle is absent.
 
6. Order: Apternygiformes:
 
Ex: Apteryx (Kiwi), Newzealand bird
 
  1. These are flightless, terrestrial birds.
  2. Wings are rudimentary.
  3. Eyes are small.
  4. Neck and legs ve small.
  5. Hind limbs bear 4 toes.
  6. These are Nocturnal. They feed on insects.
  7. Eggs are largest relatively.
  8. These are present only in Newzeland and Australia.
 
7. Order: Tinamiformes:

Ex: Tinamus.
 
  1. These are small, terrestrial with little power of flight.
  2. Wings are short and round.
  3. Pygostyle is reduced.
  4. Eggs are big.
  5. They eat plant products.
 
2. Super Order: Impennae:

This super order includes flightless aquatic birds.
 
  1. Their foreKmbs are modified into paddles.
 
This super order includes only one order.
 
1. Order: Sphenisci formes (SPHENISCI FORMES):
 
Ex: Aptenodyts (Penguin)
 
  1. These are flightless aquatic birds.
  2. Feathers are small scale like. They cover the. entire body.
  3. Forelimbs are modified into paddles. They are useful for swimming
  4. Limbs are 4 toes.
  5. Below the skin thick layer of fat will be present.
 
AptenodytsPenguin thumb17

3. Super Order: Neognathae:
 
  1. This sub order includes modern flying birds.
  2. Teeth are absent.
  3. Wings are well developed.
  4. Sternum shows keel.
  5. Flight muscles are well devebped.
  6. Pygostyle is present.
 
This super order is divisible into the following orders.
 
1. Order: Gaviformea

Ex: Gavia immer (Common loon)
 
  1. These birds show powerful fight
  2. Toes are webbed.
 
2. Order: Podlcipit formes:
 
Ex: Podiceps.
 
  1. These are fresh water birds.
  2. Feet are lobed.

3. Order: Procellariiformes:

Ex: Puffinus (Petrels, Diomedia ) ( Wandering albatross)
 
  1. Skull shows large nasal gland.
  2. Feathers are compact.
  3. Wings are long and narrow.
 
4. Order: Pelecaniformee:

Ex: Pelecanus (Pelecan)
 
  1. Aquatic fish eating birds.
  2. Four toes are webbed.
 
5. Order: Clconiformee:

Ex: Ardea (great blue heron)
 
  1. Neck is long and Legs are long
  2. Web is absent.
 
6. Order: Ariseriformea:
 
Ex: Anser domesticus (Duck), Cygnus (swan)
 
  1. Beak is broad.
  2. Tongue is fleshy.
  3. Legs are short.
  4. Feet are webbed.
 
7. Order: Faiconl forme:
 
Ex: Mihms migrans (Kite). Pseudogyps (Vulture)
 
  1. Beak is short and curved.
  2. Feet show curved daws.
  3. They are strong fleers.
 
kite thumb19
 
8. Order: Galliforroea:
 
Ex: GaOus (Jungle Fowl), Pavo cristatus (Peacock)
 
  1. Beak is short.
  2. Terrestrial birds.
  3. They will fly.
 
9. Order: Gruiformes:
 
Ex: Grus (crane)
 
  1. They are small or medium large-size birds.
  2. They may be weak or strong fliers.
  3. Legs are long.
 
10. Order: Diatrymiformee:
 
  1. These are extinct birds.

11. Order: Chardriiforrae:
 
Ex: Larus (Gull)
 
  1. Shore dwelling aquatic birds.
  2. Toes are webbed.
 
12. Order: Columbiformes:

Ex: 1. Columba livia (Pigeon), 2. Sterptopelia (Dove)
 
  1. Skin thick and soft.
  2. Beak is usually short and slender.
  3. Crop produces pigeon milk to feed the young ones.
 
ColumbaliviaPigeon thumb11
 
13. Order: Cuculiformee:

Ex: 1. Cuculus (cuckoo), 2. Eudynamis (Koel)
 
  1. Many Cuckoos are parasites.
  2. The females lay their eggs in the nests of other birds.
  3. The toes are four in number.
  4. Tail is long.
 
14. Order: Paitiaciforme:

Ex: Psittacula eupatra (Parra keet)
 
  1. Feathers are green, blue, yellow.
  2. Beak is short and curved.
  3. Frugivorus forms.
 
15. Order: Strlgiformes:

Ex: Bubo bubo (green horned owl)
 
  1. Head is large and narrow.
  2. Retina contains many rods. Hence it can see in the night time.
  3. They are nocturnal predators.
 
16. Order: Caprimulgiformee:
 
Ex: Caprinulgus (Night jar)
 
  1. Legs are weak.
  2. Beak is small.

17. Order: Apodiformes:
 
Ex: Swift (Humming bird)
 
  1. These are small birds.
  2. They are powerful fliers.
 
18. Order: Coliifbrmee:
 
Ex: Cobus (Mouse bird)
 
  1. Small birds.
  2. Tail is long.
 
19. Order: Coraci formes:
 
Ex : Akedo king fisher and hornbill
 
  1. Beak is strong. It is useful to catch fishes.
  2. Third and Fourth toes are fused at the base.
 
20. Order: Piciforme:

Ex: Brachypternus (Wood pecker), Dinopium (Wood pecker)
 
  1. Tail feathers are pointed.
  2. Beak is stout.
 
21. Order: Passed formes:
 
Ex: 1 Passer domesticus (Sparrow), Corvus (Crow), Acridotherus (Myna)

GENERAL CHARACTERS OF BIRDS (AVES)

Written by Saturday, 01 July 2017 16:57
AN INTRODUCTION TO AVES (BIRDS)
 
Birds (AVES) are highly evolved vertebrates. In the Jurassic period of Mesozoic era the Birds first appeared. They evolved from Ornithischian dinosaurs of Reptilian group. In the cretaceous period the birds became modernized.
 
Birds are bipedal vertebrates. Their fore limbs are modified into wings. Their body is covered by feathers. Hind limbs are strong and they are useful to walk on land. All these characters taking into the consideration in classification of birds.
 
Birds are adopted for aerial mode of life. Hence the body shows many modifications for aerial mode of life:
 
The science which deals with birds is called Ornithology. (Also read Branches of Biology)
 
Birds and reptiles are grouped together in “sauropsida” group.

In the present day world 8590 species of birds are living.

GENERAL CHARACTERS OF BIRDS (AVES)

Aves belongs to
 
  • Phylum: Chordate
  • Sub Phylum: Vertebrate
  • Group: Gnathostomata
  • Class: Aves
 
Birds arose in the Jurassic period of mesozoic era. Reptiles and Birds are combindly called “Sauropsida”. Birds have become highly, modified due to aerial life and show many differences from Reptiles. The present day living birds are represented by 8,590 species. They are aerial, terrestrial and aquatic.
 
birds aves types thumb24
 
  1. Birds are warm blooded, bipedal, feather clawed vertebrates.
  2. Birds body is divisible into head, neck, Trunk and Tail.
  3. In Birds Forelimbs are modified into wings (forelimb bears three cIaw less digits wings bear feathers. They are useful for flying.
  4. In Birds Hind limbs are strong and are useful to walk. They show 4 toes (Neognathae).
  5. In Birds the wings have no glands, except preen glands or oil gland present at the base tail. It secrets of the oily substance which keeps the feather waterproof.
  6. In Birds Skull is monocondylic.
  7. In Birds the lower jaw is made by 5 to 6 bones.
  8. The modern birds have no teeth.
  9. In Birds bones are spongy and pneumatic. They are light In weight end strong. They are use full for flying.
  10. In Birds Posterior caudal vertebrae will united arm a pygostyle. It acts as a rudder. During the flying it helps to change the direction of movement.
  11. Sternum is broad. It shows a keel. This keel is useful for the attachment of muscles.
  12. The clavicle and inter clavicle unite to form V shaped furcula. This will keep the wings away.
  13. In the forelimbs carpals and metacrpals are united to form carpo-metacarpus. Like that — hind limbs tarsal and metatatarsals, united to form Tarso metatarsus.
  14. The birds digestive system is well developed crop chamber is present. It stores food. Stomach is divided into glandular proventriculus and muscular gizzard
  15. In birds Anus is absent. Cloaca present. This cloaca is 3 chambered.
  16. In birds Respiratory system is well developed. The lungs are spongy.
    They are non distensible sacs around the lungs. Nine air sacs are present. They are usefull for make body light.
    a) lnterr cavicular air sac (1)
    b) 1 pair of cervical (2)
    c) 1 pair of anterior thoracic air sacs (2)
    d) pair of posterior thoracic air sect (2)
    e) 1 pair of abdominal air sacs. (2)
    They are useful or double respiration. They are also use Make to the body light.
  17. At the base of tracheae a syrinx is present. I has no vocal cords
  18. Birds or Aves Heart is four chambered..Right arotic arch is present.
  19. R.B.C. are oval, nucleate and biconcave.
  20. In birds (aves) Renal parallel system is reduced, or vestigial.
  21. Birds Kidneys are meta nephrlc. Each kidney is Three lobed. Ureters open into cloaca. Urinary bladder is absent.
  22. Birds Eyes are well developed. Monocular vision. In the eye comb plate or pecten is present. It protects the retina from sunlight. It also increases the vision.
  23. Birds Brain is well developed. Cerebral hemispheres and cerebellum are,12 pairs of cranial nerves are present.
  24. Sexes are separate - Sexual dimorphism is clearly exhibited.
  25. In the female left ovary and left oviduct are
  26. Fertilizing is internal.
  27. Birds are oviparous. They lay big sized eggs.
  28. During Embryo development extra embryonic membranes
  29. 13 vertebrae in pelvic region unite to form synsacrum.
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