All snakes except the purely aquatic ones move by means of the abdominal seutes. No snake can heap from the ground, though the more active sometimes hurl themselves from bough to bough, o• down to the ground. The vertebrae are extremely numerous, sometimes nearly 300, and are concave in front and convex behind, connected by free ball-and-socket joints, and provided with complicated processes, one effect of which is to prevent any considerable vertical motion. Every vertebra except the atlas bears a pair of ribs, articulating by the eapit ular head only, and united at their ventral ex tremities (in the absence of any sternum) by cartilages attached to the gastrosteges. The ribs admit of much movement and have an extensive and powerful musculature. The bones of the skull are not soldered together (except those of the but are loosely joined by elastic cartilages. The two halves of the lower jaw are connected by a ligament so loose and elastic Snakes have a well-developed nervous system, and are intelligent. Many may be tamed and show docility and regard for their friends. Most of them are very timid and harmless, endeavor ing to frighten their enemies by menacing atti tudes (see HOGNOSE) or otherwise. Even the well-armed poisonous ones, though sullen and resistant, are rarely aggressive. All have good eyes, and some of the many nocturnal forms very large ones; hut the eyes have no lids and are not movable. No external ear is present, but a com plicated internal apparatus exists, so that snakes hear very well and are affected by musical sounds. The sense of taste is probably deficient, but that of smell is acute, and many serpents, as the American blaeksnake, hunt largely by scent. Many serpents lay eggs, but most venomous ones, and many of our commonest species, are vivi parous. The young are ready to take care of themselves as soon as they escape front the egg, but are usually guarded for a time by the mother.
A very remarkable means of livelihood and of defense among snakes is the poison apparatus with which one large group (Solenoglypha) and some members of the generally harmless Colubri der are provided. This consists of a pair of very large labial glands, one beside each upper jaw. modified from parotid salivary glands. and eon saliva imbued with an alkaloid poison, likely to be fatal to all animals into whose cir culation it enters. (See illustration.) These fangs are of three kinds. They may be the most for ward of the maxillary teeth in the upper jaw.
immovable and deeply grooved on the anterior side, as in the cobras and others of the Protero glypha ; or they may be thus fixed and grooved, but posterior in position (Opisthoglypha) ; or they may be lengthened and the maxillary bone so hinged as to dip down, al lowing the fangs when not in use to lie hack in a fold of the gum (where there are no other teeth) ; and the fang-groove may be closed over for most of its length, forming a canal opening near the point of the tooth, as in vipers and rattle snakes. This contrivance in sures the conveyance of the poison into the deepest part of the wound. When the snake is about to bite. the month is opened very wide, the fangs are unsheathed, swung forward and held fixed by muscular contraction, and then sunk into the flesh of the victim with a marvelously sudden and swift forward and downward stroke. Sec ondary and partly involuntary action of other muscles presses the poison out of the gland and through the duet and tooth. The venom will sometimes exude and drip from the fangs of a snake excited and ready to strike, and some of this may be blown forward by the forcible ex pulsion of the animal's breath: but the stories of `spitting poison' have no better foundation than this. For the nature. effects, and antidotes of snake poison, see TOXICOLOGY.
The older families of snakes are eircumtropi cal, and none are found where a really cold eli mate prevails. The great family Colubridte is cosmopolitan, as also is the Boida', being absent only from NOV. Zealand, which, like most oceanic islands, has no serpents at all, zind from the colder latitudes. Their near allies, the Ambly cephalida% are altogether Oriental and Malayan. The Viperida• (including the crotaline group) are cosmopolitan, but no true vipers occur in America, whereas smile erotalines are found in Southern Asia, although all the rattlesnakes proper are American. The number of species of snakes is about 1800.
Snakes perform :in important part in preserv ing the balance of life, for all are carnivorous, and prey principally upon insects and the small animals, mostly rodents, which tend to multiply excessively. They are, therefore, of great service to agriculture in keeping down the hordes of in jurious locusts, mice, gophers, and the like, which afflict the farmer. Their flesh is white, chicken like, and wholesome, and is eaten by savage peo ples, and occasionally by persons in civilization who are free front the traditional prejudice.