PHYLUM CHORDATA 



445 



In the lizard (Fig. 268) and crocodiles there is a cross- 

 shaped membrane-bone, the interclavicle or episternum (epist), 

 in relation to the pectoral arch and sternum. In the limb- 

 less lizards the pectoral arch may be absent or may be well 

 developed ; it is completely wanting in all snakes. In the 

 pelvic arch the ischium is separated from the pubis by a wide 

 space not developed in the Amphibia. Slight vestiges of hind- 

 limbs occur in some pythons alone among the Ophidia. 



JVa La- 



Fig. 267. — A, lateral view of skull of rattlesnake fCrotaluS). B. O, basi-occipital; 

 B. S, basi-sphenoid; E. O, exoccipital; F. O, fossa ovalis; La, conjoined lac- 

 rymal and pre-frontal; L. /, articulation between lacrymal and frontal; Mn, 

 mandible; Mx, maxilla; Na, nasal; PI, palatine; Pmx, pre-maxilla: P. Sph, 

 pre-sphenoid; Pt, pterygoid; Qu, quadrate; ^.squamosal; /A /', foramina 

 of exit of the second and fifth cranial nerves. R, transverse section at point 

 lettered B in Fig. A; T, trabecular. (After Huxley.) 



In the lizards teeth are present in the pre-maxilla?, the 

 maxillae, the mandible, and usually the palatines. These 

 are in most lizards small and simple, and uniform in shape 

 and arrangement. A Mexican Lizard, Heloderma, which 

 also occurs in Utah and Arizona, differs from all the rest in 



