CROCODILIANS. LIZARDS, AND SNAKES. 165 



petrosal, while above it joius the alisphenoid, and to a less degree the 

 parietal. In its junction with the petrosal it overlaps that bone so 

 far as to almost exclude it from the external wall of the brain case, and 

 it can only be seen by looking within the posterior border of the tri- 

 geminal foramen. The alisphenoid is well developed, and joins above 

 thedecurved border of the parietal posteriorly, the postfrontal medially, 

 and the frontal anteriorly. The alisphenoids meet on the middle line, 

 leaving a large foramen above for the rhinencephalon, and a large 

 8-shaped foramen below. The inferior part of the latter is immediately 

 posterior to the keel-like anterior process of the sphenoid. A strong 

 process descends to the pterygoid, bounding the trigeminal foramen in 

 front. This represents the epipterygoid of the Sauria. No orbito- 

 sphenoid or other interorbital bone. 



The anterior half of the basioccipital has its longitudinal axis verti- 

 cal. The long axis of the sphenoid is also vertical. The medullary 

 part of the brain case is roofed by the exoccipitals only, but the supra- 

 occipital bounds the epencephalon above. The petrosal is much more 

 conspicuous on the internal than on the external wall of the brain case. 

 It is suboval, and is bounded by the alisphenoid, sphenoid, exoccii)ital, 

 supraocciijital, and to a small degree by the parietal. It is deeply 

 notched in front by the trigeminal foramen. Although the sphenoid is 

 mainly vertical in position it sends forward between the alisphenoids 

 a vertically compressed plate, already mentioned. The occipital and 

 sphenoid elements are coarsely cellular at various points. The ptery- 

 goids unite together on the median line and join the sphenoid behind 

 the posterior nares. The pterygoids send forward a i)rocess above the 

 palatines to the front of the orbits, where they cease. Here a strong 

 X)rocess of the prefrontal descends on each side and rests on the adja- 

 cent iiarts of the palatine and pterygoid. These processes are separate 

 on the middle line above and below, but touch at the middle of their 

 length. The ectopterygoids are large and each sends a process forward 

 on the maxillary, and a longer one on the pterygoid. The palatine and 

 maxillary bones are in nuitual contact on the middle line, and no jjart 

 of the vomer or ethmoid is visible on the external surface. 



The mandibular ramus has a rather elongate angle, which has its 

 superior concave surface divided lengthwise by an obtuse ridge. The 

 articular bone forms the greater part of the angle, the angular being a 

 narrow strip on its inferior side, which forms the apex, the surangular 

 sending a narrow splint on the external side, which does not extend so 

 far as the two other elements. The cotylus is not divided by a ridge, 

 but a transverse section is gently sigmoid, descending inward. The 

 coronoid is a large scale in front of the very large dental foramen, and 

 does not extend anterior to the vertical line of the angular. A large 

 foramen is inclosed between the latter and the spleuial. The latter 

 element forms the entire internal side of the ramus, terminating acutely 

 below and within the fourth tooth. The groove in front of its apex is 



