142 



VERTEBRATE SKELETON 



but here and there small bones (possibly orbitosphenoidal) may occur 

 in it. Perforation of the septum is common. 



Other cranial bones are the sep to maxilla ries (conchas, fig. 150), one on either 

 side in the floor of the nasal capsule and between the organ of Jacobson and the 

 nasal septum, these occurring in lizards, Sphenodon, Phytosaurs and some Thero- 

 morphs, some of the latter having an 'infranasal bone.' 

 Some Orthopodous Dinosaurs have an unpaired 'rostral 

 bone' in front of the premaxillae. 



Fig. 150. — Dia- 

 grammatic cross- 

 section of nasal 

 skeleton of snake 

 (Biitschli, '10). w, 

 nasal; s, septomax- 

 illary; v, vomer. 



The lower jaw is supported by the quadrate 

 which is connected with the cranium by other 

 bones, most prominent of which is the squamosal, 

 which plays no part here in the cranial wall. It 

 overlaps the quadrate more or less completely behind 

 (the extreme occurring in turtles, fig. 155), either 

 holding it firmly (Monimostylica) or allowing it to 

 play on the cranium (Streptoslylica). In most 

 recent reptiles the squamosal articulates with the parietal and often 

 with the parotic process of the exoccipital and opisthotic, the prootic 

 sometimes contributing to the process. Many Theromorphs have 

 a supratemporal. The quadrate itself is large except in most 

 Theromorphs. 



Meckel's cartilage often persists in the lower jaw until old age, its 

 posterior end ossifying as the articulare. The two halves of the jaw 



Fig. 151. 



-Medial side of lower jaw of Varanus. a, articulare; an, angulare; c, coro- 

 noid; d, dentale; g, goniale; sa, surangulare; sp, splenial. 



are united by cartilage or suture at their anterior ends, except in 

 Ophidia where there is a ligamentous connexion, permitting a wide 

 distension of the mouth, and in Chelonia and Anomodonts where the 

 halves are ankylosed. In the extreme development there are many 

 membrane bones in the lower jaw (fig. 151). On either side of the 

 anterior end of the Meckelian is a dentale, followed on the medial 

 side by a splenial. At the insertion of the occludent muscles is a 

 coronoid, and on the outer ventral side an angulare, dorsal to which 

 is a surangulare. A goniale occurs on the medial and ventral side 



