PLATES AND SCALES OF A TYPICAL SNAKE.

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1. Side view of head of a colubrine snake; 2, front view: 3, top of head; 4, under side of head and throat; 5, vent and anal plates; 6, side of a part of the body. Numbers and letters: e, eye; n, nostril; 1, rostral plate; 2, nasal; 3, loreal; 4, preocular or anteorbital; 5, postocular or postorbital; 6, temporal; 7, internasal; 8, prefrontal; 9, frontal; 10, superciliary or supraocular; 11, parietal; 12, notch in rostral for protrusion of tongue; 13, labial: 14, infralabials; 15, gular; 16, mental; 17, submental; 18, abdominal scutes or gastrosteges; 19, dorsal scales; 20, keeled body scales; 21, unkeeled lateral scales; 22, divided anal scute covering anus; 23, wrosteges.

the face, and then is peeled off by the animal scraping through a crevice or a fold of its own body; even the coating of the eye is included.

that they are capable of separation to a great extent. The teeth are simple, sharp, curved backward and solidly fixed in sockets. When broken or lost they are renewed. There are typically two rows on the upper jaw and two on the palate (maxillaries, palatines, and pterygoids), and each mandible of the lower jaw bears a single row; but vipers and rattlesnakes have none in the upper jaw except the poison fangs, which are depressible at will and fold back out of the way of food entering the mouth. The process of swallowing is laborious. With a large victim this process may last for hours, the head and throat be stretched to almost bursting, and the snake become nearly exhausted by its efforts. A great amount of saliva is poured out in this process, but the story that snakes cover their prey with slime before swallowing it is a fable.

Most snakes are carnivorous. Small mammals, frogs, reptiles, and insects form the bulk of the diet of ordinary land species. Some of them eat eggs, and a few species are fond of milk. Many of them are of great assistance to the agriculturist by devouring the grasshoppers, mice, gophers, and other pests of the farm in great numbers. The stomach is long and narrow, as also are the lobes of the liver. Snakes drink much water when in active life; yet they possess no urinary bladder. The intestines are highly absorbent. The heart is placed well forward. The lungs are elongated, and when bilobed, as in boas and rattlesnakes, one lobe is far larger than the other. The trachea is long, is provided with air sacs, and opens far forward in the mouth, all of which arrangements guard against suffocation during the tedious process of swallowing. The forcible expulsion of air from the trachea makes the hissing sound which is the serpent's only vocal utterance; but the bullsnake has special tracheal arrangements (see illustration) by which its hiss may be increased. to a sort of bellow.

NASAL APPENDAGES OF HERPETON.

No

All snakes except the purely aquatic ones move by means of the abdominal scutes. snake can leap from the ground, though the more active sometimes hurl themselves from bough to bough, or down to the ground. The vertebræ 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 capitular head only, and united at their ventral extremities (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 brain-case), but are loosely joined by elastic cartilages. The two halves of the lower jaw are connected by a ligament so loose and elastic

MOUTH OF A SNAKE.

Open mouth of the bull or pine snake (q.v.) showing the (black) tongue and opening of the windpipe: a, sheath of the tongue; b, epiglottis; c, glottis.

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 attitudes (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; but the eyes have no lids and are not movable. No external ear is present, but a complicated 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