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 limbs or pectoral girdle. There are no temporal arches, no squamosals, jugals, epipterygoids, 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 interrupted by the coalescent optic foramina. Proötics largely visible. The pterygoids and usually the palatines have teeth. The premaxillae are small and often edentulous; maxillae rarely edentulous. Teeth acrodont. Parietals fused, no parietal foramen. The mandibles 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, sometimes to the caudals with a more or less prominent hypapophysis. No chevrons, but more or less of the caudals with a descending process on each side (lymphapophyses).
This suborder, often considered an order, includes more than eighteen hundred living 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 terrestrial 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 altogether; and of them with very few exceptions their fossil remains are few and fragmentary, and their taxonomic relations very doubtful.
