THE SUBCLASS PARAPSIDA 275 



B. Suborder Ophidia (Serpentes) 



Elongated, legless reptiles of from a few inches to thirty feet in 

 length, sometimes with vestiges of hind limbs but never with front 

 Umbs or pectoral girdle. There are no temporal arches, no squa- 

 mosals, jugals, epiptery golds, lacrimals, postoptics, and sometimes 

 no ectopterygoids. The quadrate articulates loosely with the tabular 

 only; in a few instances even the tabular is absent (Uropeltidae) . 

 The brain-case in front is enclosed by descending plates from the 

 parietals and frontals to the sphenoid, from the latter sometimes in- 

 terrupted by the coalescent optic foramina. Prootics largely visible. 

 The pterygoids and usually the palatines have teeth. The premaxil- 

 lae are small and often edentulous; maxillae rarely edentulous. 

 Teeth acrodont. Parietals fused, no parietal foramen. The man- 

 dibles are united in front by ligaments only ; the posterior bones are 

 often fused, the coronoids sometimes absent, the dentaries loosely 

 articulated. The vertebrae are numerous, sometimes exceeding four 

 hundred in number, divisible into precaudal and caudal series, the 

 first two or three without ribs, cervical. Always procoelous and 

 always with zygosphenes and zygantra. Anterior vertebrae, some- 

 times to the caudals with a more or less prominent hypapophysis. 

 No chevrons, but more or less of the caudals with a descending proc- 

 ess on each side (lymphapophyses) . 



This suborder, often considered an order, includes more than 

 eighteen hundred Hving species widely distributed over the earth. 

 Like so many groups of organisms known in many related forms, 

 there is scarcely a single positive character to distinguish them ; the 

 most decisive, as has been mentioned, is probably the complete bony 

 closure of the brain- case; and there is never a vestige of a pectoral 

 girdle, though several families have vestigial pelvic and hind limb 

 bones. Probably the snakes are the latest group of equivalent rank 

 to be evolved among the Reptilia, and of the snakes the poisonous 

 vipers are probably among the latest. Most snakes are purely ter- 

 restrial in habit; a few are burrowing, and still others are aquatic. 

 And chiefly because of such upland habits they are very scantily 

 represented among fossils, not more than fifty or sixty species alto- 

 gether; and of them with very few exceptions their fossil remains are 

 few and fragmentary, and their taxonomic relations very doubtful. 



