324 



ZOOLOGY 



SECT. 



like appearance owing to the development of processes of 

 the squamosal and occipital regions, which unite above the 

 posterior part of the cranial roof. The skull of the Amphisbsenians 

 differs from that of other Lacertilia and approaches that of Snakes 

 in the absence of an inter-orbital septum. 



In the skull of the Ophidia (Fig. 932) orbito-sphenoidal and 

 alisphenoiclal elements are absent, their places being taken by 

 downward prolongations of the parietals and frontals. In the 



B 



Art- 



Fov 



FIG. 932 Skull of Colubrine Snake (Tropidonptus natrix). A, from below ; B, from above. 

 Ag. angular ; Art. articular ; Bp. basi-occipital ; Bs. basisphenoid ; Ck, internal nares ; 

 Cocc. occipital condyle ; Dt. dentary ; Eth. ethmoid ; F, frontal ; F', post-orbital ; F. or. 

 Fenestra ovalis ; F. ^."parietal foramen ; Jug. jugal ; M. maxilla ; N. nasal ; Osp. supra-occipital 

 taking the place of orbito-sphenoid ; P. parietal ; PC. prootic ; P. /. pre-frontal ; PL palatine ; 

 Pmx. pre-maxilla; Pt. pterygoid ; 01. exoccipital ; Qu. quadrate; SA. supra-angular; 

 Squ. squamosal ; Ts. transverse ; Vo. vonier ; //, optic foramen. (After Wiedershcini.) 



substance of the mesethmoid are two cartilaginous tracts (Fig, 

 933, B, T) which are the persistent trabeculse of the foetal skull. 

 The inter-orbital septum is absent, and the cranial cavity is 

 prolonged forwards to the ethmoidal region. The palatines 

 ( PI) are movably articulated with the base of the skull ; as in 

 the Lizards they are widely separated from one another, and do 

 not develop palatine plates. They are movably articulated 

 behind with the pterygoids (P), and, through the intermediation 

 of the slender transverse bones (Ts), with the maxillae. The 

 pre-maxilla3 are very small (in some venomous Snakes entirely 

 absent), and when present usually fused together. The maxilla^ j~), 

 usually short, articulate by means of a movable hinge-point with 



