FOSSIL REPTILES. 283 



even be averred that it is comprised in the paries of the cra- 

 nium; and this paries has also sometimes in the thickness of its 

 membranes a point of ossification which truly represents the 

 temporal wing. M. Cuvier, who regards it altogether as a new 

 and peculiar bone, has given it the name of columella. Its ob- 

 ject is to support the vault of the cranium, which is not sup- 

 ported in front, because the orbital and temporal wings and the 

 ethmoid are in a great measure membranous. 



The lateral occipital gives out a projecting part externally, to 

 which are united by their extremity the mastoidean, which is 

 much reduced, and the temporal bones. To this common 

 junction of these three bones is suspended the tympanic bone, 

 which descends vertically to serve as a pedicle to the lower jaw. 

 This bone, for the most part, gives attachment only to the 

 anterior edge of the tympanum ; and the rest of the contour of 

 that membrane, as well as the hinder paries of the cavity, is 

 cartilaginous, or simply membranous. 



The Eustachian tube is merely a wide communication from 

 the cavity into the back part of the mouth, between the extre- 

 mity of the pterygoidean and the sphenoid. In the fresh 

 animal it corresponds to the inside of the mouth, near the 

 articulation of the jaws ; and the communication is sometimes 

 so open, that one can scarcely tell whether the auricular osselet 

 is in the mouth, or in the pharynx. 



The cavity of the vestibulum is formed in common by the os 

 petrosum, the lateral, and upper occipitals. The fenestra 

 ovalis, where the auricular osselet is attached, is common to 

 the 0.9 petrosum and the external occipital. Under it is a 

 wider opening, pierced in the lateral occipital only, and at the 

 bottom of which are two foramina ; one, anterior, which goes 

 into the cranium ; the other, posterior, which is the fenestra 

 rotunda, and opens into a fosset of the vestibulary cavity which 

 represents the cochlea. 



A transverse bone unites the pterygoid to the jugal, and to 

 the maxillary, as in the crocodile. 



