xm PHYLUM CHORDATA 325 



the lacrymal (La\ which, in turn, is movably connected with the 

 frontal. The long and slender quadrate (Qu) is freely articulated 

 with the posterior end of the elongated squamosal. The rami of 

 the mandible, likewise long and slender, are not united anteriorly 

 in a symphysis, but are connected together merely by elastic liga- 

 mentous 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 Typhlopidae differ from the rest of the Ophidia in having the 

 maxillaB immobile, the quadrate more closely connected with the 



FIG. 933. A, lateral view of skull of Rattlesnake (Crotalus). B. 0. basi-occipital ; B. S 

 basi-sphenoid ; E. 0. exoccipital ; F. 0. fossa-ovalis ; La conjoined lacrymal and pre-frontal ; 

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

 PI. palatine ; Prux. pre-maxilla ; P. Sph. pre-sphenoid ; Pt. pterygoid ; Qu. quadrate ; Sq- 

 squamosal ; //, V, foramina of exit of the second and fifth cranial nervsa ; B, transverse 

 section at point lettered B in Fig. A ; T. trabeculse. (After Huxley.) 



skull, and the rami of the mandible united by a fibro-cartilaginous 

 symphysis. 



The skull of Hatteria (Fig. 934) differs from that of the Lizard 

 mainly in the following points. There is a large superior temporal 

 fossa bounded by the parietal, post-orbital (P. or), and squamosal, 

 and separated below by a bar of bone (superior temporal arch) formed 

 of processes of the last two bones 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 (Ju), with a small quadrato-jugal, by which the jugal is con- 

 nected with the quadrate. The quadrate (Qu) is immovably fixed, 

 wedged in by the quadrato-jugal, squamosal, and pterygoid. The 

 pre-maxillse (Pmx) are not fused together, but separated by a* suture. 



In the Chelonia (Figs. 935, 936) all the bones, including the 

 quadrate, are solidly connected together. There is an inter- 



