462 



COMPAEATIVE ANATOIMY. 



In most Saurii (and in Chelys among tlie CMonii), as in the 

 Birds, the premaxill^ are fused together; in the latter they are 

 distinguished "by the possession of a long frontal process. Their 

 size is correlated with that of the beak_, the form of which is largely 



due to the share 

 - fl that they take in it. 



They are rudimen- 

 tary in the Ophidii 

 (Fig. 249, C Px) 

 and small in the 

 Chelonii. The max- 

 illa therefore forms 

 the greater portion 

 of the boundary 

 of the edge of the 

 lower jaw (Mx) ; 

 this bone is of great 

 size in the Croco- 

 dilini and Saurii, 

 and very large in 

 the Ophidii, in 

 which also it is 

 capable of a large 

 amount of move- 

 ment. 



There is a lateral 

 series of bones at- 

 tached to the quad- 

 rate. The first of 

 these is the quad- 

 rato-jugal ; this is 

 absent in the Ophi- 

 dii. In the Saurii 

 it is connected with 

 the quadrate at the 

 point where this 

 bone is united to the skull. It is continued forwards into a second 

 piece, which is partly connected with a post-frontal, and partly 

 with a jugal which passes round the lower edge of the orbit. In 

 Birds the quadrato-jugal (Fig. 250, JB Qj) is a slender piece of 

 bone, which arises from the side of the mandibular joint of the 

 quadrate. In the Chelonii and Crocodilini it is connected with a 

 larger portion of the quadrate, and supports the jugal, which aids in 

 bounding the orbit. 



In all cases the lower jaw is articulated to the quadrate, and is 

 made up of the same parts as in Fishes, to which, however, a supra- 

 angular and a complementary bone are added on. 



In the Chelonii and Aves the two dentaries fuse very early ; in 

 Birds the other bones retain indications merely of their primitive 



Fig. 251. View of the base of the skulL A Of Chelonia. 

 B Of Crocodilus. 01 Basi-occipital. 01 Esoccipital. 

 C Occipital condyle. Sph Basi-sphenoid. 02J0 Opisthotic. 

 Ft Pterygoid. Pal Palatine. Vo Tomer. Q Quadrate. 

 Qj Quadratojugal. Tr Transverse. Mx Maxilla. Px Pre- 

 maxilla. Pa Parietal. Pfr Post-frontal. Fr Frontal. 

 Ch Posterior nares. E Eustachian tube. 



