OPHIDIA OR SERPENTS. 229 



and saurus, a lizard, and briefly describes these strange 

 forms. The body resembles that of an ordinary mam- 

 mal, the jaws and teeth those of a crocodile ; and the wings 

 remind us of those of a bat. The fifth or little finger is 

 exceedingly elongated, thus affording a support for a mem- 

 brane, which, with the arm, made a wing for flying. The 

 principal genus is Pterodactylus (Fig. 262), and it includes 

 species of various sizes, from those having a spread of three 

 feet, like some of those found in the Old World, to some 

 of the gigantic species (Pterodactylus ingens, Marsh) in 

 the Cretaceous rocks of the central portion of the United 

 States, which have a spread of twenty.-five feet ! 



SUB-SECTION VIII. 

 THE ORDER OF OPHIDIA OR SERPENTS. 



SERPENTS are scaly reptiles which are exceedingly elon- 

 gated and without feet, and whose skull and jaws, verte- 

 brae and ribs, make up the whole skeleton both sternum 

 and sacrum being wanting. A pair of slender bones, how- 

 ever, often supporting a second bone armed with a claw, 

 are found suspended in the flesh near the hind part of 

 the body, in some species ; these are regarded as the rudi- 

 ments of hind limbs. 



The vertebrae in serpents are exceedingly numerous, 

 and articulate with each other not only by a cup and ball 

 on the central portion of the vertebrae that is, on the cen- 

 trum but also by eight joints in addition to these, which 

 interlock by parts reciprocally receiving and entering into 

 one another ; and thus the vertebral column is very strong, 

 while at the same time it has great freedom of motion. 

 Moreover, as the danger is greatest of being crushed by 



