.352 



ZOOLOGY 



SECT. 



roof formed of expansions of the post-frontals (ph) parietals (par) 

 and squamosals (sq.) with the jugal (/) and quadrato-jugal (q.f). 

 The immovably fixed quadrates (Fig. 992, qu, and Fig. 991, q) are 

 modified to afford a part or the whole of the rim for the support 

 of the tympanic membrane. The occipital condyle is triobed. The 

 vomer (v) is unpaired. The palatines (pal) are approximated and 

 give off palatino plates, which for a short distance cut off a nasal 



passage from the cavity of the 

 mouth. Nasals are usually ab- 

 sent as separate bones. The pre- 

 maxillae are very small. The 

 rami of the mandibles are stout, 

 and are firmly united together 

 at the symphysis. 



In the Crocodiles (Figs. 993, 

 994), as in the Chelonia, the 

 quadrate (Qu) is firmly united 

 with the other bones of the skull. 

 There is a membranous and car- 

 tilaginous interorbital septum. 

 There are no distinct orbito- 

 sphenoids, but alisphenoids are 

 well developed. The orbit is 

 separated from the lateral tem- 

 poral fossa by a stout bar situated 

 somewhat below the surface, and 

 formed of processes from the 

 post-frontal, jugal and ectoptery- 

 goid. The lateral temporal fossa 

 is bounded below, as in Spheno- 

 don, by an inferior temporal arch 

 composed of jugal and quadrato- 

 jugal. The frontals are early 

 united into one, and the same 

 holds good of the parietals. An 

 ectopterygoid is present. Both 

 palatine (PI) and pterygoid (Pt),. 

 as well as maxillae, develop 

 palatine plates in the roof of the 

 mouth, cutting off a nasal passage 

 of great length from the cavity of the mouth, the posterior 

 nares (ch) being situated far back towards the posterior end 

 of the cranial base. The nature of the articulation between 

 the mandible and the quadrate is such that movement is re- 

 stricted to the vertical plane, and lateral displacement is further 

 provided against by the development of a broad process of the 

 pterygoid against which the inner surface of the mandibular 



FIG. 903. Skull of Crocodilus porosus, 

 dorsal view, x about J. Col, buttress 

 connecting the post-frontal with the jugal 

 and ectopterygoid ; F. frontal ; Jg. jugal ; 

 MX. maxilla ; Na. nasal ; P. parietal ; 

 Pm. premaxilla ; Po.f. post-frontal ; Pr.f. 

 prefrontal ; Q. quadrate ; Qj. quadrato- 

 jugal ; R. characteristic ridge on the 

 prefrontal bone ; Sq. squamosal ; T. per- 

 foration in the premaxilla caused by a 

 pair of lower incisor teeth. (After Gadow.) 



