THE SKULL 



93 



KIT 



in which they are replaced functionally by strong horny sheaths 

 on the edges of the jaws. The teeth may be borne on the 

 palatine and pterygoid, as well 

 as on the maxilla, premaxilla 

 (which is usually unpaired), 

 and dentary. 



In the young Hatteria only 

 amongst existing Reptiles do the 

 vomers bear teeth (usually one on 

 each). In certain fossil forms brush - 

 like masses of sphenoidal teeth 

 were present. 



The remarkable horned skull of 

 the gigantic Ceratopsidce (Diiio- 

 sauria) which reached a length of 

 nearly seven feet, possessed horny 

 beaks in addition to teeth oil the 

 maxilla and dentary. A parietal 

 foramen w T as present. 



In correspondence with 

 the absence of branchial re- 

 spiration during development, 

 the branchial apparatus plays 

 no great part in Reptiles, and 

 often only the slightest traces 

 of it are seen : thus in Snakes, 

 for instance, only the hyoid 

 remains, and this not always. 

 In Chelonians a basal piece 

 ("basihyobranchial") as well 

 as the first branchial arch per- 

 sist in addition (Fig. 76). 



FIG. 76. HYOBRANCHIAL APPARATUS 

 WITH LARYNX AXD TRACHEA or Emys 

 europcea. 



ZH, basihyobranchial, which widens at 

 ZB and bears the cricoid (RK) and 

 arytenoid (AK) cartilages of the 

 larynx; KH, lesser hyoicl cornua; 

 ZH, greater hyoid cornua ; IK, first 

 branchial arch ; TV, trachea. 



E. Birds. 



The skull of Birds is formed on a similar plan to that of 

 Reptiles more particularly of Lizards, but it exhibits certain 

 special characteristics (Fig. 77). 



The brain-case is proportionately very large, and all the cranial 

 bones show a tendency to run together by the obliteration of the 

 sutures originally present between them ; they are usually delicate 

 and spongy (" pneumatic "), thus contrasting greatly with those of 

 Reptiles. 1 



Only in the region of the nose does the cartilage persist 

 throughout life to any extent, and even here not always. 



1 It should, however, be mentioned that the development of air spaces 

 within the bones of the skull is hinted at in Crocodiles and certain fossil 

 Reptiles. 



