118 COMPARATIVE ANATOMY 



surrounded by bones, and in some forms (e.g. Cheloiie, Sphargis) the 

 whole temporal region is covered by an additional roof, above the 

 cranial roof proper, formed by the parietal, squamosal, and post- 

 frontal. An ossification between the pterygoid and a descending 

 lamella of the parietal (which latter boric forms part of the wall of 

 the cranial cavity) apparently represents an epipterygoid. The 

 palatines give rise to palatine plates, which together with lateral 

 parts of the median voiner help in forming a short hard-palate. 

 The opisthotic remains distinct from the exoccipital, and the pre- 



'Cccc 



FIG. 84. SKULL OF YOUNG WATER-TORTOISE (Emys euro/urn). Side view. 



BP, cartilaginous interval between basioccipital and basisphenoid ; f 1 , post- 

 frontal ; UK, horny sheaths of jaws ; /, point of entrance of the olfactory 

 nerve into the nasal capsule ; In;/, jugal ; Aid, mandible ; Mt, tympanic mem- 

 brane ; Na, external nostril ; 0*p, supraoccipital, which gives rise to a crest ; 

 Pf, pref rental, which forms a great part of the anterior boundary of the 

 orbit ; (Jju, paraquadrate (" quadrate- jugal") ; Si, interorbital septum. Other 

 letters as in Fig. 83. 



maxilla is usually paired, while the dentaries are united at the 

 symphysis. No indications of a parasphenoid are known, and 

 a transpalatine is wanting. 



There are no teeth, which are replaced functionally by horny 

 beaks, as was also the case in certain fossil Reptiles (e.g. Cerato- 

 psidre). 



The hyobranchial skeleton is comparatively large, and consists 

 of a body, very closely related to the larynx and produced 

 anteriorly into a short lingual process, of a pair of small hyoid 

 cornua, and of two pairs of larger cornua belonging to the first 

 and second branchial arches (Fig. 85). 



Crocodilia (Fig. 86). The chondrocranium is less fenestrated 

 than in Lizards, and a basipterygoid process is not strongly 

 marked : the interorbital septum, which is inserted vertically 

 between the anterior parts of the trabeculas, attains a consider- 

 able development. Alisphenoids are present. 



The bones are very massive and firmly united together by 

 sutures : those on the dorsal and lateral regions are pitted. 



