XIII 



PflYLUM CHORDATA 



.".4<» 



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

 merely by elastic ligamentous tissue, so tliat, 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 anotlier. The Typhlopida' differ from the rest of the 

 Ophidia in having the maxilln' immobile, the ([uadrate more closely 

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

 a fibro-cartilaginous symphysis. 



The skull of Sphenodon (Fig. 900) differs very considerably 

 from that of the Lizards. There is a large sv.pra-temiwral fossa 

 bounded by the parietal, post-orbital (Ft. J), and S([uamosal, and 

 separated below by a bar of bone {superior temporal arch), formed 



Fio. 080. — A, lateral view of skull of Rattlesnake (Crotalus). B. 0. basiocsipital ; B. S. 

 l)a.si.spheiiiiid ; E.O. oxoccipital ; F. 0. fenestra ovalis : La. eoujoined laorynial and pre- 

 frontal; L. f. articulation Vietween laerjuiial and frontal; ila. niandilile ; itx. nvixilla ; 

 Na. n.asal ; PI. palatine; Pinp. prcmaxilla ; P. S/ik. prcsphenoid ; Pt. jiturytfi'id ; Qii. 

 quadrate ; Sij. .squamo.sal ; //, K, foramina of exit of the second and fifth cranial nerves ; 

 B, trau-sverse section at point lettered B in Fig. A ; T. trabecule!. (After Huxley.) 



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

 fi'ontal, from a still larger space — the hitcnd temporal fos-sa. The 

 latter is bounded below by a slender bony bar (the inferior te/tn2Joral 

 arch), formed of the long narrow jugal (Jug), 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 and squamosal. 

 The quadrate (Qu) is immovably fixed, wedged in by the qiiadrato- 

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

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

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



