1. premaxilla. 2. nasal. 3. frontal. 4. parietal. 5. supra-occipital. 6. epiotic. 7. prootic. Immediately in front of the figure 7 is the prominent foramen for the trigeminal nerve. 8. opisthotic. 9. basioccipital. 10. quadrate. 11. pterygoid. 12. basisphenoid. 13. alisphenoid. 14. prefrontal. 15. vomer. 16. maxilla. 17. palatine. 18. dentary. 19. splenial. 20. angular. 21. supra-angular. 22. articular. 23. coronoid. 24. exoccipital. 25. squamosal. 26. jugal. 27. external mandibular foramen. 28. internal mandibular foramen. VIII. internal auditory meatus. XII. hypoglossal foramen.] [Illustration: FIG. 24. DORSAL VIEW OF LOWER JAW OF ALLIGATOR (_A. Mississippiensis_). 18. dentary. 19. splenial. 21. supra-angular. 22. articular. 23. coronoid.] The _basioccipital_ (14) which, as has been said, forms a small part of the ventral wall of the foramen magnum, consists of a heavy dorsal portion, the ventrally curved condyle, and of a broader, irregular ventral portion, between which and the basisphenoid is the single opening of the Eustachian canals (eu). Dorsally and laterally the basioccipital articulates with the exoccipitals; ventrally, laterally, and anteriorly with the basisphenoid which was described in the lateral view. _The Sagittal Section_ (Fig. 23). The only bones shown in this figure (besides those of the mandible, to be described later) that have not already been described are the vomers and those of the auditory capsules. The _vomers_ (15) are delicate bones articulating with the maxillæ, the palatines, the pterygoids, and with each other. They form a part of the septum and roof of the nasal passage. The _mesethmoid_ is not ossified. Reynolds describes the bones of the auditory capsules as follows: “Three bones, the _epiotic_, _opisthotic_, and _pro-otic_, together form the auditory or _periotic_ capsule of each side. They are wedged in between the lateral portions of the occipital and parietal segments and complete the cranial wall in this region. Their relations to the surrounding structures are very complicated, and many points can be made out only in sections of the skull passing right through the periotic capsule. The relative position of the three bones is, however, well seen in a median longitudinal section. The _opisthotic_ early becomes united with the exoccipital, while the _epiotic_ similarly becomes united with the supraoccipital, the pro-otic (Fig. 23, 7)--seen in longitudinal section to be pierced by the prominent _trigeminal foramen_--alone remaining distinct throughout life. The three bones together surround the essential organ of hearing which communicates laterally with the deep tympanic cavity by the _fenestra ovalis_.