XITI 



PHYLUM CHORDATA 



349 



are not united anteriorly in a symphysis, but are connected together 

 merely by clastic ligamentous tissue, so that, when the mouth of 

 the Snake is opened to allow of the entry of the relatively large prey, 

 which it swallows whole, they are capable of being widely separated 

 from one another. The Typhlopida; differ from the rest of the 

 Ophidia in having the maxilke immobile, the quadrate more closely 

 connected with the skull, and the rami of the mandible united by 

 a fibre-cartilaginous symphysis. 



The skull of Sphenodon (Fig. 990) differs very considerably 

 from that of the Lizards. There is a large supra-temporal fossa 

 bounded by the parietal, post-orbital (Pt. /), and squamosal, and 

 separated below by a bar of bone (superior temporal arch}, formed 



Fin. 989. A, lateral view of skull of Rattlesnake (Crotalus). B. 0. basioccipital ; B. S. 

 basisphenoid ; E. 0. exoccipital ; F. 0. fenestra ovalis ; La. conjoined lacryroal and pre- 

 frontal ; L.f. articulation between lacrymal and frontal ; Mn. mandible; MX. maxilla; 

 Nit. nasal ; PI. palatine ; Pmp. premaxilla ; P. Sph. presphenoid ; Pt. pterygoid ; QH. 

 quadrate ; Srj. squamosal ; //, 7, foramina of exit of the second and fifth cranial nerves ; 

 B, transverse section at point lettered B in Fig. A ; T. trabeculsw. (After Huxley.) 



of processes of the two last-mentioned bones and of the post- 

 frontal, from a still larger space the lateral temporal fossa. The 

 latter is bounded below by a slender bony bar (the inferior temporal 

 arch), formed of the long narrow jugal (7i^),with a small quadrato- 

 jugal, by which the jugal is connected with the quadrate (Q). The 

 lateral temporal fossa is separated from the orbit in front by a bar 

 of bone formed of the jugal and post-orbital, and is bounded behind 

 by a posterior temporal arch formed of the parietal arid squamosal. 

 The quadrate (Qii) is immovably fixed, wedged in by the quadrato- 

 jugal, squamosal and pterygoid. The premaxillse (Pmx) are not 

 fused together, but separated by a suture. There is a broad palate 

 formed by the plate-like vomers, palatines, and pterygoids. 



