EUSUCHIA 435 



basisphenoid, immediately behind the posterior symphysis of the 

 dorsal portion of the pterygoids, which latter almost completely 

 cover the basisphenoid. The vomer is not visible (except in Caiman 

 niger), being covered by the ventral junction of the palatines 

 and maxillaries. The broad, lateral wings of the pterygoids 

 are connected by separate bones, the ectopterygoids = trans- 

 palatines = transverse bones, with the maxillaries, and in recent 

 forms also with the jugals. Thus an extensive, very firm bony 

 palate is produced ; and the large palatal foramina, between the 

 palatines, maxillaries, ectopterygoids and pterygoids, are closed 

 by the same dense mucous membrane which cover the whole 

 roof of the mouth. 



The opisthotic and epi-otic bones fuse early with the lateral 

 and with the supra-occipital bones ; only the pro-otic remains 

 longer as a separate element, perforated anteriorly by a large 

 hole for the exit of the third branch of the trigeminal nerve. 

 The basisphenoid is scarcely visible, being covered by the 

 pterygoids. The presphenoid is large, continued forwards and 

 upwards into the usually cartilaginous interorbital septum. 

 Near the anterior and upper margin of the presphenoid is a 

 large notch on either side for the passage of the optic nerve, the 

 three eye-muscle nerves and the first branch of the trigeminal 

 nerve. There are no separate orbito-sphenoids, their place being 

 taken by membrane or cartilage in continuation with the inter- 

 orbital septum, but the alisphenoids are large, abutting upwards 

 against the frontals. Each prefrontal sends down a vertical 

 process which joins the palatine of its side. 



The configuration of the snout varies much. There are two 

 parallel lines of development since the Jurassic epoch, namely, 

 long-snouted creatures, of which two still survive as Gavialis and 

 Tomistoma, and more broad and short-snouted members like the 

 rest of the Crocodiles and Alligators. In opposition to the 

 Parasuchia the elongation of the snout is effected by the 

 maxillaries. The length of the nasals varies much, mostly in 

 conformity with that of the maxillaries. As a rule they reach 

 the premaxillaries but not always the nasal groove. In Gavialis 

 they are short, far separated from the premaxillaries by * the 

 maxillaries, which meet in the dorso-median line. The orbit is 

 bordered by the frontals, which at an early age fuse into an un- 

 paired piece, and by the prefrontal, lacrymal, jugal, and postfrontal. 



