462 



C0MPAKAT1VE ANATOMY. 



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

 Birds, tke premaxillaB 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 

 - B that they take in it. 



Tkey are rudimen- 

 tary in tke Opkidii 

 (Fig. 249, Px) 

 and small in tke 

 Ckelonii. Tke 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 tke Croco- 

 dilini and Saurii, 

 and very large in 

 tke Opkidii, in 

 wkick also it is 

 capable of a large 

 amount of move- 

 ment. 



There is a lateral 

 series of bones at- 

 tacked to tke quad- 

 rate. Tke first of 

 tkese is tke quad- 

 rato-jugal ; tkis is 

 absent in tke Opki- 

 dii. In tke Saurii 

 it is connected with 

 tke quadrate at tke 

 point wkere tkis 

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

 piece, wkick is partly connected witk a post-frontal, and partly 

 with a jugal wkick passes round tke lower edge of tke orbit. In 

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

 bone, wkick arises from tke side of tke mandibular joint of the 

 quadrate. In tke Ckelonii and Crocodilini it is connected witk a 

 larger portion of tke quadrate, and supports tke jugal, wkick aids in 

 bounding tke orbit. 



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

 made up of tke same parts as in Fiskes, to wkick, kowever, a supra- 

 angular and a complementary bone are added on. 



In tke Ckelonii and Aves tke two dentaries fuse very early; in 

 Birds tke otker bones retain indications merely of their primitive 



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

 B Of Crocodilus. Ob Basi-oceipital. 01 Exoecipital. 

 C Occipital condyle. Spb Basi-sphenoid. Qpo Opisthotic. 

 Pi Pterygoid. Pal Palatine. Vo Vomer. Q Quadrate. 

 Qj Quadratojngal. Tr Transverse. Mx Maxilla. Pa Pre- 

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

 Ch Posterior nares. E Eustachian tube. 



