Fig. 43. Palatal aspect A, of the cranium, B, of the mandible of an Alligator (Caiman latirostris). × 1/3. (Brit. Mus.)

1. premaxillae.12. quadratojugal.
2. maxillae.13. quadrate.
3. palatine.14. dentary.
4. pterygoid.15. splenial.
5. posterior nares.16. coronoid.
6. transpalatine.17. supra-angular.
7. posterior palatine vacuity.18. angular.
8. anterior palatine vacuity.19. articular.
9. basi-occipital.20. lateral temporal fossa.
10. opening of median21. openings of vascular canals
Eustachian canal.leading into alveolar sinus.
11. jugal.

The cartilage and membrane bones of the cranium proper when taken together can in most vertebrates be seen to be more or less arranged in three rings or segments called respectively the occipital, parietal and frontal segments; in the Crocodile however only the occipital and parietal segments are clearly seen.

The occipital segment consists of four cartilage bones, three of which together surround the foramen magnum.

The most ventral of these, the basi-occipital (figs. 43 and 45, 9), forms the single convex occipital condyle for articulation with the atlas, bounds the base of the foramen magnum, and is continuous laterally with two larger bones, the exoccipitals (fig. 45, 24), which meet one another dorsally and form the remainder of the boundary of the foramen magnum. Each is drawn out externally into a strong process, which is united below with the quadrate, and above with the squamosal by a surface seen in a disarticulated skull to be very rough and splintered. In a longitudinal section the anterior face of the exoccipital is seen to be closely united with the opisthotic.

The exoccipital is pierced by a number of foramina, four lying on the posterior surface. Just external to the foramen magnum is a small foramen for the exit of the hypoglossal nerve (figs. 44 and 45, XII). External to this is the foramen for the pneumogastric (fig. 44, X), while more ventrally still is the foramen (fig. 44, 15) through which the internal carotid artery enters the skull. Some distance further to the side, and more dorsally, is a larger foramen which gives passage to the facial nerve and certain blood-vessels.

In a median longitudinal section of the skull the hypoglossal foramen is seen, and just in front of it a small foramen for a vein. Further forwards the long slit-like opening between the exoccipital and opisthotic is the internal auditory meatus (fig. 45, VIII) through which the auditory nerve leaves the cranial cavity and enters the internal ear.

The supra-occipital (fig. 45, 5) is a small bone which takes no part in the formation of the foramen magnum, and is closely united in front with the epi-otic. It is characteristic of Crocodiles that all the bones of the occipital segment have their longer axes placed vertically, and that they scarcely if at all appear on the dorsal surface.

In front of the occipital segment is the parietal segment. The dorsal and ventral portions of the two segments are in contact with one another, but the lateral portions are widely separated by the interposition of the auditory and suspensorial bones.