The hard parts of the animal body are collectively known as skeletal system or simply skeleton. The vertebrates possess the hard parts inside the body. It is known as endo skeleton. The endo skeletal structures are formed with cartilages and bones which are the living tissues. The endo skeleton has been divided into:

I. Axial skeleton - includes the skull and vertebral column.

II. Appenducular skeleton - includes the girdles and limb bones.

preavious topic: Respiration in birds-reptiles-mammals

The skull develops in the head of animal body. The skull includes two major parts - 'Cranium' enclosing the brain and the organs of special sense and Visceral arches' which form the jaws and frame work of pharyngeal wall.

The cranium is developed from the mesodermal cells soon after the appearance of the brain. It is also known as brain box. Cranium includes three pairs of capsules for smell, sight and hearing. These are known as olfactory, optic and auditory capsules respectively. The cartilaginous cranium is called chondro cranium and bony cranium is called dermato cranium.

The visceral arches develop around anterior (Pharyngeal) part of the embryonic gut from the cells of neural crests. Mostly seven visceral arches are present. The first one is the largest and highly modified - 'Mandibular arch. It has dorsal & ventral halves. Each side of the dorsal half is termed the palato -pterygoid Quadrate Cartilage. It bears teeth and forms the upper jaw. The ventral half of the mandibular arch is called Meckel's cartilage. It also bears the teeth and form the lower jaw. The wide gap between the two jaws is the mouth. The two jaws articulate their hind ends by hinge joints which enable the mouth to open & close. The second arch is hyoid arch and the remaining five arches are termed bronchial arches. The visceral arches are collectively known as the splanchno cranium. The upper jaw and lower jaw are known as Maxilla and Mandible respectively: 







1. First incisors


Foramen magnum

2. Second incisors



3. Nasal


Paroccipital process

4. Premolars


Aperture of External Auditory meatus

5. Vomer


Tympanic bulla

6. Palatine



7. Supra orbital process of frontal


Pitutory foramen

8. AbsphenokJ


Sphenoidal fissure

9. Zygomatic process of squamosal



10. Basioccipital



11. Eustachian canal



12. Periotic


Zygomatic Process of Maxilla

13. Foramen Lace rum Posterius



14. Occipital Condyle


Palatine Process of Premaxilla

I5. Supra - occipital




SKULL OF Scoliodon (Shark) SKULL OF Rana (Frog) SKULL OF Calotes(garden lizard) SKULL OF Columba (Pigeon) SKULL OF Oryctolagua (Rabbit)
1.  Skull is formed with cartilage tissues. 1.  Skull is formed most­ly with bony tissues (but tadpole skull is cartilaginous) 1. Skull is formed most­ly with bony tissues. 1.   Skull is formed mostly with bony tissue. 1. Skull is formed with ' mostly bony tissue.
2.  It consists of crani­um, sense capsules and visceral arches. 2.  It consists of cran­ium, sense capsules, jaws and hyoid ap­paratus. 2. It consists of crani­um, sense capsules, jaws and hyoid apparatus. 2.   Same as in calotes. 2. Same as in calotes.
3.  It is the axial portion of the skull. It is more or less a violin box open in front and be­hind with an arched roof and flattened floor. It is divided into occipital, auditory, orbital and ethmoidal regions. 3.  It forms the middle hollow part of the skull. It is divided into auditory, olfactory and occipital regions. 3. It forms the median hollow part of the skull. It is divided into occipital, audi­tory, orbital, olfacto­ry and optic regions. 3.   It forms the posterior median hollow part of the skull. It is divided into occipital, audito­ry, optic orbital and ol­factory regions. 3. It forms the middle hollow part of the skull. It is divided into occipital auditory, optic orbital & olfac­tory regions.
4.  Foramen magnum is posteriorly present. 4.  Same. 4. Same 4.   Same 4. Same
5. Beneath the foramen magnum a deep concavity is present. On either side of this concavity is a pro­minence - occipital condyle articulates with the first verte­bra, occipital crest is formed. Dicondylic skull. 5.Beneath the foramen magnum there are two occipital con­dyles. On either side Of the foramen mag­num dorso-laterally exoccipital bones are present. Dicondylic skull 5.Beneath the fora­men magnum a sin­gle occipital condyle is present.suupraoccipitai, exo occipitals,& basi occipital bones are also present in the occipital region. Monocondylic skull. 5.Beneath the foramen magnum single occip­ital condyle is present. Supra occipital, Exocci pitals & basioccipital bones are also present. Monocondylic skull. 5.Beneath the fora­men magnum two occipital condyles with paroccipital process are present. Supraoccipital, exo-ccipitai, & basio-ccipital bones are also present. Dico­ndylic skull.
6.   Auditory region has a mid dorsal depres­sion - parietal fossa. It contain two pairs of apertures. Anteri­orly smaller open­ings of endolymp­hatic ducts and pos­teriorly larger open­ings of perilymphatic spaces are present. 6.— 6.-- 6.    - 6.    –
7.Auditory capsules lie on the poster lat­eral sides of the cranium. Which enclose & protect the ears. Post orbital groove is present on the ven­tral side 7. Auditory capsules enclose the internal ear. Its roof is formed by pro-otic bone, fenestra ovalis, sta­pedial plate and columella auris are present. 7.  Each auditory capsule is formed by small, single vertical prootic bone which is lying outside the supra occipital. Epiotic & opisthotic are not differentiat­ed. 7.    Each auditory capsule is formed largely by the prooticbone. Fenestra ovalis, fenestra rotun da, columella auris, stapes are also present. 7.Each auditory cap­sule in the adult an­imal consists only periotic. Flask - like Tympanic bulla bone is significant.
8.  - 8.Dorsally the cranium is formed, by frontoparietals, ven­trally by parasphenoid and laterally by sphen ethmoid bones. 8.  The dorsal part of the cranium is formed by parietals, frontals interparietal foramen, and ven­trally by basisphenoid,parasphenoid bones. 8.  The dorsal part of the cranium is formed by Parietals, frontals a rostum, alisphenoids; ventrally basisphenoid, basitemporal bones. 8.   The cranium is formed dorsally by 'Parietals, frontals, inter parietal, and ventrally by basisphenoids, presphenoid bones along with alis-phenoids and orbit.07 sphenoids. The cra­nial cavity is closed infront by a narrow vertical bone cibriform plate.
9.   Each orbit lies on the sides of the middle part of the cranium. It is bordered by dor­sal super orbital ridge,anterior preorbital process, posterior post orbital process and ventraily by infra orbital ridge. The or­bital region has a large oral cavity anterior fontanelle. 9. On either side of the cranium is large gap - orbit which lodges the eye. 9.  9.In the middle of the cranium laterally two orbits are present. Each orbit is bounded by prefrontal supra orbital, lacri­mal, post frontal and jugal bones. The jugal bone forms the ventral border of the orbit. Supratemporal arch is present. 9.  The two orbits are very large cavities present infront of the cranium. Each orbit is bounded dorsally by frontal, antero - dorsally by lac­rimal and posteriorly by the zygomatic process. Orbit is incomplete on the ventral side. The two orbits are separated by inter orbital septum. 9.   These are two orbits are large sockets present on the sides of frontal segment of cranium. The orbit is bounded dorsally by frontal, anteriorly by maxilla and lacrimal, posteriorly by squa­mosal and alisp-henoid and external­ly by the zygomatic arch.
10.  The olfactory cap­sules lie at the anteri­or side of the cranium. Each capsule possesses a short sic at ethmopalatine ridge 10.    The olfactory cap­sules are separated, from each other by mesethmoid. Each capsule is formed by a large triangular nasal on the dorsal side and a smaller triradiate vomer on the ventral side vomers possess vomerine teeth. 10. Each olfactory capsule is formed by three bones Nasal, septo maxillary and vomer. 10. Each olfactory capsule is formed by two bones - Nasal and vomer. Nasals fuse with
frontals and form into
super and inferior pro-
10.  Each olfactory cap­sule is bounded by dorsally by long na­sal bone and laterally by jaw bones. The two capsules are sep­arated by mesethmoid bone. The lower end of mesethmoid fits into a vomer bone. Vomer is formed by the fusion of a pair of bones.
11,Ethmoidal region tapers anteriorly. It consists of a basal slender barventro-median rostral carti­lage and a pair of sim­ilar barsdorso - lateral rostral cartilages aris­en from the roof of ihe olfactory capsules. 11.    Absent. 11. Absent. 11. Absent. 11.  Absent.
12.  Scoliodon has seven visceral arches which are cartilagienous. The first arch forms the jaws and it is catted Mandibular arch the second one is the hy-oid arch the remain­ing five arches are called branchial arch­es. 12. Branchial arches are absent.There are upper and lower jaws to support the borders of the mouth. The upper jaw is formed by union of two similar halves. Each half is formed by the Pre-maxilla, maxilla and quadratojugal. The inner set of the jaw has palatine, ptery goid and squamosal bones. The lower consists of two halves and unite an­teriorly by mento-meckelian cartilage. Each half consists of dentary and angio -splenial bones. Just infroni of the articu­lar fact a small coro-nary process is present. Upper jaw alone has teeth. 12. Branchial arches are absent. 12. Branchial arches are absent. 12.   Branchial arches ab­sent.These are upper and lower jaws. Each half of the upper jaw is formed by premax-illa, maxilla jugular, palatine, pterygoid and squamosal.
13.  The mandibular arch consists of two halves. Each half of this arch possess an upper paleto-pterygo quadrate cartilage and a lower meckel s cartilage.The pale-topterygo Quadrate gives off anteriorly palatine. The two sides of it from the upper jaw with teeth. The two meckel's cartilages united antero medially by lig­ament form the lower jaw with teeth.   13. These are upper and lower jaws. Each half of the upper jaw consists of an outer set of bones - pre maxilla, maxilla, jugal and quadrate and the inner set in­cludes pterygoid, palatine, transp-alatine, epiptery-goid and squamo­sal. Each half of the lower jaw consists of six bones -dentary, angular, supra angular, ar­ticular, splenial and coronoid. Both the jaws possess teeth. 13. These are upper and lower jaws. Each half of the upper jaw is formed by premaxil-la, maxilla, quadra -tojugal, and jugal bones. The inner ar­cade of the upper jaw forms the roof of bucco pharyngal cav­ity which consists of palatine, pterygoid, and quadrate. Each half of the lower jaw is formed by articu­lar, angular supra an­gular, dentary and splenial. Both the jaws are lacking the teeth. 13.The lower jaw also con­sists of two halves. Each half is formed by a single, large dentary bone. The posterior of the dentary possess con­dylar, coronoid and angular process. Both the jaws pos­sess the codent type of teeth which are having different (Heterodont teeth in mammals) shap­es. Diastema is present in both the jaws because of the absence of canines.
14. Hyostylic jaw sus­pension. 14. Auto stylic jaw sus­pension. 14. Auto stylic jaw sus­pension. 14. Autostylic jaw sus­pension. 14. Craniostylic jaw suspension.