. SERPENTS, Ophidat, an order of reptiles, which is in general simply characterized as having a very elongated body and no external limbs. The links, however, which unite saurians with .serpents are very numerous; the limbs of many saurians being partially wanting, and little more than rudimentary; whilst limbs are found by anatomical examination in many serpents, and the rudimentary hinder limbs of sonic, as boas, appear externally in the form of hooks or claws. See BOA.
The body and tail are covered with scales, the head often with plates. The vertebrfe and ribs are extremely numerous, a pair of ribs being attached to each vertebra through out the N\ hole length of the body. •Some serpents have more than 300 pair of ribs. The ribs not only serve to give form to the body, and aid in respiration, but are also organs of locomotion. There is no breast-bone (sternum) for the small end of the ribs to be attached to, as in other vertebrate animals, but each rib is joined by a slender cartilage and a set of short muscles to one of the scales of the abdomen. A serpent moves by means of the ribs and of these scales, which take hold on the surface over which it passes, and in this way it can glide—often very rapidly—along the ground, or on the branches of trees; and many species climb trees with great facility, gliding up them as if on level ground. Most—if not all—of the species are also capable of elevating a great Portion of the body from the ground; and many of those which live among the branches of trees hold their place firmly by means even of a few scales near the tail, and freely extend the greater portion of the body in the air. On a perfectly smooth surface, as that of glass, a serpent is quite helpless, and has no power of locomotion.
The vertebra of serpents are so formed as to admit of great pliancy of the which is capable of being coiled up, with the head in the center of the coil, and some serpents have the power of throwing themselves to some distance from this coiled posi tion. The vertebra: are articulated by perfect ball-and-socket joints, the anterior extremity of each rounded into a smooth and polished ball, which fits exactly into a hemispherical cup in the next; but there are processes in each vertebra which prevent any motion except from side to side, so that serpents are quite incapable of the vertical undulations so often represented in prints. The ribs are also attached to the vertebrae by ball-and-socket joints.
Cuvier divided serpents into three sections, the first—of which the common blind worm (q.v.) or slow-worm of Britain is an example—consisting of those which have the skull, teeth, and tongue similar to those of saurians, and in which the eye has three lids, and there are vestiges of bones of anterior limbs; the second. which Cuvier calls true serpents, having no vestiges of such bones; the eye destitute of lids, and the bones of the head so formed that the mouth and throat are capable of very great dilation; the third, which lie calls naked serpents, containing only the genus ececilia (q.v.), now known, not withstanding its form, to belong really to the batrachians or amphibia.
The serpents of Cuvier's first section have been conjoined with some of the nearly allied saurians, more or less furnished with external limbs, under the name saurophidia, by Mr. Gray. They are connected with the true serpents by the families amphisbcenidar and typhlopsithr, which nearly agree with them in the structure of the head and mouth. but want the third eyelid—some of the typhlopsidce, indeed, having the eye itself merely rudimentary—and, like the true serpents, have no vestige of breast-bone or shoulder. These, with all the creatures included in this section, are, in so far as is known, perfectly harmless. They lire chiefly on insects and other very small animals.
The true serpents live on larger prey, which they swallow entire, some of them—as the boas—crushing it by constriction in the coil of their muscular body. The prey of a serpent is often thicker than the serpent itself, and to admit of its being swallowed, the throat and body are very dilatable. The bones of the head are adapted to the necessity of n great expansion of the mouth and dilation of the throat. The bones composing the upper jaw are loosely joined together by ligaments; and even the arches of the palate are movable. "The two halves of the lower jaw are connected by a ligament, so loose and elastic that they are capable of separation to a great extent; and the mastoid and tympanic bones, which connect the lower jaw and the skull, are lengthened out into podicels, allowing an extraordinary power of dilation. Serpents, however, sometimes seize prey too big for them to swallow, and die in the attempt, their teeth being so formed as to render it difficult to reject by the mouth what has once got into' the throat.