Serpent, Or Snake, the common name of the ophidian reptiles, including, according to the earlier naturalists, all air-breathing oviparous vertebrates, of elongated and rounded body, without limbs and creeping on the ventral surface. The body is very flexible and narrow, without distinct neck and with conical tail; bones of the face movable, making the mouth very dilatable; teeth sharp, separate, usually hooked on both jaws and almost always on the palate; no eyelids, nor tympanum, nor apparent external auditory foramen; skin extensible, protected by thin scales covered by an epidermis which is shed in a single piece by a process of inversion; the plates of the under surface are larger, and used for progression; the male reproductive organs are double, concealed, and capable of protrusion, which has led some to the belief that snakes have posterior limbs; they are oviparous, and a few are ovoviviparous, and the young undergo no metamorphosis after leaving the egg. The spine consists of very numerous and movable vertebrae, concave in front and hemispherically convex behind, distinguishable only into costal and caudal; the occipital condyle is single, and the jaws are connected by a very movable interarticular bone; the very numerous ribs are always distinct and free at the lower end, there being no sternum nor pectoral arch.

The tongue is soft and fleshy, protractile, deeply forked, and held in a sheath; the visceral organs are very long, closely fitting in the abdominal cavity; only a single lung well developed, generally the left, forming a cavity with spongy walls, and the hinder portion frequently without cells, its simple sac serving probably as a reservoir of air; opening of the cloaca transverse. The vertebrae are rarely fewer than 100, and in some boas and pythons as many as 400, presenting the largest number among animals; progression is almost always by lateral undulations, the ribs with their attached ventral plates being so many pairs of feet, like those of myriapods, in some boas more than 300 pairs; the anterior limbs are wanting, but in some boas and pythons there are horny hooks appearing externally, supported on a rudimentary pelvic arch; with these few exceptions posterior limbs are wanting. Most of the muscles are specially adapted for acting on the spinal column, and are arranged in a very complicated manner, especially those in connection with the ribs. The brain is small, and the spinal cord very long, with exceedingly numerous vertebral nerves.

For other details of structure see Compara-tive Anatomy, and Reptiles. They creep, spring, climb, swim, constrict, suspend themselves by the tail, burrow, and raise the body almost erect. Like most reptiles, they are very sensitive to cold, becoming lethargic in winter; the muscular irritability is remarkably great and persistent, depending on the spinal nervous agency and the inherent property of the muscular tissue; the heart palpitates long after it has been removed from the body, and the jaws open and shut in the decapitated head. The senses of smell, hearing, and taste are very imperfect; the eyes, without lids and constantly open, appear immovable; the principal seat of touch is in the soft and extensile tongue. The scales offer every variety of color and marking, but in most the general color resembles the objects on which they habitually live; the coloring matter is in the middle layer of the skin, the inner or dermis being strong and holding the scales, and the outer or epidermis shed several times a year; the animal is dull and does not eat at the period of casting its skin.

These characters are sufficient to distinguish serpents from large annelids, eel-like fishes, the scincoid and chal-cidian saurians, and many elongated batrachi-ans; they are reptiles in the true sense of the word. For the systems of classification see Herpetology; they are generally divided into the two groups of the venomous and non-venomous; the first, like the cobra, rattlesnake, and viper, have movable fangs in the upper jaw communicating with a poison gland. All feed on living prey, which is swallowed whole; while some are rapid in pursuit, others crush their victims to death, or poison them, or bring them within reach of their jaws by a kind of fascination, terrifying by their hideous and menacing aspect some of the active and smaller mammals and birds into a momentary loss of power. They eat and drink rarely, and are capable of sustaining very long fasts; digestion is performed very slowly; the secretion of the large salivary glands is profuse. For details on the poison apparatus see Cobra de Capel-lo, Rattlesnake, and Viper. The stomach is little more than a prolongation of the oesophagus, and the intestines are very short; the heart is in a fibrous pericardium, and consists of two auricles, and one ventricle with two unequal apartments communicating with each other; hence a mixed arterial and venous blood is sent over the system; the growth is slow, and the life prolonged; the hissing attributed to serpents is a faint sound produced by the slow escape of air through the mouth or nostrils during expiration, and only exceptionally would be noticeable by an indifferent observer; the animal heat is low.

The males are smaller, more slender, brighter, and more active than the females; no nest is made, there is no incubation (except in the python) by the heat of the body, no food is stored up for the young, and no education nor parental care is necessary. The mother hides the eggs in a suitable place, and leaves them to be hatched by the heat of the sun and air; sometimes the young are brought to maturity in the mother's body, as in the vipers. There are about 1,000 described species, widely distributed over the world, especially in the warmer regions; doubtless many varieties from age, sex, and climate have been described as species. - Fossil remains of serpents have been found in all the divisions of the tertiary age; paloeophis (Owen), attaining a length of 20 ft., has been found in the eocene of England, showing a higher temperature than now exists in N. Europe; many more species, probably belonging near the genus coluber (Linn.) if not in it, are met with in the middle and upper tertiary and the diluvium of Europe. Prof. Marsh describes in the "American Journal of Science" (1870) the dinophis grandis from the New Jersey tertiary greensand, a vertebra of which indicated an animal 30 ft. long, allied to the present marine boas.

Almost all the species older than the post-pliocene are related to the constrictors. He draws attention to the fact of the occurrence of closely related large serpents in the same geological formations in Europe and in this country, just after the disappearance of the snake-like mo-sasaurus and its allies, interesting in view of the probable derivation of the serpents. Other large species have since been described in the same journal. - For interesting information on serpents, see Broderip's "Note Book of a Naturalist," part 13, and F. Buckland's "Curiosities of Natural History" (London, 1859).