OPHIDIA 



239 



ORDER II. OPHIDIA 



Snakes are considered degenerate lizards, and by some zo- 

 ologists are classed with the lizards, and the group together 

 called Order Squamata. 



The Ophidians are reptiles with no fore limbs, no pectoral 

 girdle, no sternum or sternal ribs, but the ends of the dorsal 

 ribs are connected with the ventral scales, or scutes, and both 



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Fig. 197. — Rudimentary or vestigial hind limbs of python as exhibited 

 in the skeleton and on the external surface of the animal (\ natural size). 

 (Romanes.) 



scales and ribs aid in the body motion. "A snake literally 

 walks on the ends of its ribs." 



Vestiges of the hind limbs (Fig. 197) sometimes appear as Httle 

 spurs on either side of the vent. The ribs, which begin with the 

 second vertebra and continue to the end of the body, aid in res- 

 piration. They aid in locomotion also, their ventral ends fitting 

 into the "connective tissue of the sides of the ventral transverse 

 scales (scutes) ." The body is long and the vertebrae very numer- 

 ous. 



They vary in size from the enormous ones of the tropics to 

 our little green grass snakes. Some are aquatic, some terrestrial 



