Great as is the difference in appearance between a typical snake and a typical lizard, the two orders of Ophidians and Lacertilians are nearly allied; the former is probably merely a specialized descendant of the latter or of the pythonomorphous reptiles, or perhaps of both. Moreover, the living Lacertilians include forms which approach the Ophidians by having a greatly increased number of vertebrae, a much advanced degradation of the scapular and pelvic arches and limbs, a simple dentition, and the absence of eyelids and external ear-opening. And on the other hand we find Ophidians with a greatly diminished flexibility of the vertebral column, with closely adherent, smooth and polished scales, with a narrow mouth—totally unlike the enormous gape of the typical snakes—and even without that longitudinal fold in the median line of the chin which is so characteristic of the order (Typhlopidae). Thus of the Ophidian characters as given above only that taken from the loose connexion of the bones of the skull remains as a sharp line of separation between snakes and lizards. The mandibulary symphysis is not by suture but by an elastic band; the intermaxillary, palatine, and pterygoid bones are so loosely attached to the cranium that they can be easily pressed outwards and forwards, and the maxillary and mandibulary of one side can be moved in those directions independently of their fellows opposite. The intermaxillary is small, generally toothless, and coalesces with the nasals and vomer into a single movable bone; finally, the suspensory is much elongate and movable at both ends. This arrangement ensures an extraordinary degree of mobility and elasticity of all parts of the gape, which, however, varies in the different families of the order. For the other characteristic points of their structure and for their distribution, see Reptiles.

The number of known species of snakes has been given as 1500 by some authorities and as 1800 by others. The limits of their distribution seem to be the 70th parallel N. lat. in Europe, the 54th in British Columbia, and the 40th parallel S. lat. in the southern hemisphere. The number of species and of individuals in a species is small in the temperate zones, but increases as the tropics are approached. In the tropical zone they are abundant, especially where a well-watered soil nourishes a rich vegetation, with glades open to the sun, and where a variety of small animals serve as an abundant and easily obtained prey. It is in the tropics also that the largest (boas, pythons) and the most specialized kinds occur (tree snakes, sea snakes, the large poisonous snakes). On the other hand, every variety of soil is tenanted by some kind of snakes: they form a contingent in every desert fauna. In accordance with this general distribution snakes show a great amount of differentiation with regard to their mode of life and general organization; and from the appearance alone of a snake a safe conclusion can be drawn as to its habits. The following categories may be distinguished.

(1) Burrowing snakes, which live under ground and but rarely appear on the surface. They have a cylindrical rigid body, covered with generally smooth and polished scales; a short strong tail; a short rounded or pointed head with narrow mouth; teeth few in number; small or rudimentary eye; no abdominal scutes or only narrow ones. They feed chiefly on invertebrate animals, and none are poisonous. (2) Ground snakes, living chiefly on the ground, and rarely ascending bushes or entering water. Their body is cylindrical, flexible in every part, covered with smooth or keeled scales, and provided with broad ventral and subcaudal scutes. All the various parts of their body and head are well proportioned; the non-poisonous kinds of ground snakes are in fact the typical and least specialized snakes, and more numerous than any of the other kinds. They feed chiefly on terrestrial vertebrates. The majority are non-poisonous; but the majority of poisonous snakes must be referred to this category. (3) Tree snakes, which are able to climb bushes or trees with facility or pass even the greater part of their existence on trees. Their body is rarely cylindrical, generally compressed and slender; their broad ventral scutes are often carinate on the sides. Those kinds which have a less elongate and cylindrical body possess a distinctly prehensile tail. The eye is generally large. Their coloration consists often of bright hues, and sometimes resembles that of their surroundings. They feed on animals which likewise lead an arboreal life, rarely on eggs. Poisonous as λvell as innocuous snakes are represented in this category. (4) Freshwater snakes, living in or frequenting fresh waters; they are excellent swimmers and divers. The nostrils are placed on the top of the snout and can be closed whilst the animal is under water. Their body is cylindrical, moderately long, provided with narrow ventral scutes; the tail tapering; head flat, rather short; and the eyes of small size. They feed on fish, frogs, and other aquatic animals, and are innocuous and viviparous. (5) Sea snakes are distinguished by the compressed, rudder-shaped tail, supported by erect neural and haemal spines. They never leave the sea (with the exception of one genus) and are unable to move on land. They feed on fishes, are viviparous and poisonous. The majority of snakes are active during the day, their energy increasing with the increasing temperature of the air; whilst some delight in the moist sweltering heat of dense tropical vegetation, others expose themselves to the fiercest rays of the midday sun. Not a few, however, lead a nocturnal life, and many of them have, accordingly, their pupil contracted into a vertical or more rarely a horizontal slit. Those which inhabit temperate latitudes hibernate. Snakes are the most stationary of all vertebrates; as long as a locality affords them a sufficiency of food and some shelter to which they can readily retreat, they have no inducement to change it. Their dispersal, therefore, must have been extremely slow and gradual. Although able to move with extreme rapidity, they cannot maintain it for any length of time. Their organs of locomotion are the ribs, the number of which is very great, nearly corresponding to that of the vertebrae of the trunk. They can adapt their motions to every variation of the ground over which they move, yet all varieties of snake locomotion are founded on the following simple process. When a part of the body has found some projection of the ground which affords it a point of support, the ribs are drawn more closely together, on alternate sides, thereby producing alternate bends of the body. The hinder portion of the body being drawn after, some part of it (c) finds another support on the rough ground or a projection; and, the anterior bends being stretched in a straight line, the front part of the body is propelled (from a to d) in consequence. During this peculiar locomotion the numerous broad shields of the belly are of great advantage, as by means of their free edges the snake is enabled to catch and use as points of support the slightest projections of the ground. A pair of ribs corresponds to each of these ventral shields. Snakes are not able to move over a perfectly smooth surface. Thus it is evident that they move by dragging their body over the ground, or over some other firm base, such as the branch of a tree; hence the conventional representation of the progress of a snake, in which its undulating body is figured as resting by a series of lower bends on the ground whilst the alternate bends are raised above it, is an impossible attitude. Also the notion that snakes when attacking are able to jump off the ground is quite erroneous; when they strike an object, they dart the fore part of their body, which was retracted in several bends, forwards in a straight line. And sometimes very active snakes, like the cobra, advance simultaneously with the remainder of the body, which, however, glides in the ordinary fashion over the ground; but no snake is able to impart such an impetus to the whole of its body as to lose its contact with the ground. Some snakes can raise the anterior part of their body and even move in this attitude, but it is only about the anterior fourth or third of the total length which can be thus erected.

With very few exceptions, the integuments form imbricate scale-like folds arranged with the greatest regularity; they are small and pluriserial on the upper parts of the body and tail, large and uniserial on the abdomen, and generally biserial on the lower side of the tail. The folds can be stretched out, so that the skin is capable of a great degree of distension. The scales are sometimes rounded behind, but generally rhombic in shape and more or less elongate; they may be quite smooth or provided with a longitudinal ridge or keel in the middle line. The integuments of the head are divided into non-imbricate shields or plates, symmetrically arranged, but not corresponding in size or shape with the underlying cranial bones or having any relation to them. The form and number of the scales and scutes, and the shape and arrange ment of the head-

shields, are of great value in distin guishing the genera and species, and it will therefore be useful to explain in the accompanying woodcut (fig. 3) the terms by which these parts are de signated. The skin does not form eye lids; but the epi dermis passes over the eye, forming a transparent disk, concave like the glass of a watch, behind which the eye moves. It is the first part which is cast off when the snake sheds its skin; this is done several times in the year, and the epidermis comes off in a single piece.

The tongue in snakes is narrow, almost worm-like, generally of a black colour and forked; that is, it terminates in front in two extremely fine filaments. It is often exserted with a rapid motion, sometimes with the object of feeling some object, sometimes under the influence of anger or fear.

Snakes possess teeth in the maxillaries, mandibles, palatine, and pterygoid bones, sometimes also in the intermaxillary; they may be absent in one or the other of the bones mentioned. In the innocuous snakes the teeth are simple and uniform in structure, thin, sharp like needles, and bent backwards; their function consists merely in seizing and holding the prey. In some all the teeth are nearly of the same size; others possess in front of the jaws (Lycodonts) or behind in the maxillaries (Diacrasterians) a tooth more or less conspicuously larger than the rest; whilst others again are distinguished by this larger posterior tooth being grooved along its outer face. The snakes with this grooved kind of tooth have been named Opisthoglyphi, and also Suspecti, because some herpetologists were of opinion that the function of the groove of the tooth was to facilitate the introduction of poisonous saliva into a wound. The venomous nature of these snakes, however, has never been proved, and persons are frequently bitten by them without any evil consequences. Nevertheless as the depth of the groove, the length of the tooth, and the development of the salivary glands in its vicinity vary greatly, it is quite possible that the function and the physiological effect of this apparatus are not the same in all Opisthoglyphs. In the true poisonous snakes the maxillary dentition has undergone a special modification. The so-called Colubrine Venomous snakes, which retain in a great measure an external resemblance to the innocuous snakes, have the maxillary bone not at all, or but little, shortened, armed in front with a fixed, erect fang, and provided with a deep groove or closed canal for the conveyance of the poison, the fluid being secreted by a special poison-gland. One or more small ordinary teeth may be placed at some distance behind this poison-fang. In the other venomous snakes (Viperines and Crotalines) the maxillary bone is very short, and is armed with a single very long curved fang with a canal and aperture at each end. Although firmly anchylosed to the bone, the tooth, which when at rest is laid backwards, is erectile,—the bone itself being mobile and rotated round its transverse axis by muscles. One or more reserve teeth, in various stages of development, lie between the folds of the gum and are ready to take the place of the one in function whenever it is lost by accident, or shed, which seems to happen at regular intervals. The gland which secretes the poison is described under Reptiles (vol. xx. p. 457).

All snakes are carnivorous, and as a rule take living prey only; a few feed habitually or occasionally on eggs. Many swallow their victim alive; others first kill it by smothering it between the coils of their body (constriction). The effects of a bite by a poisonous snake upon a small mammal or bird are almost instantaneous, preventing its escape; and the snake swallows its victim at its leisure, sometimes hours after it has been killed. The prey is always swallowed entire, and, as its girth generally much exceeds that of the snake, the progress of deglutition is very laborious and slow. Opening their jaws to their fullest extent, they seize the animal generally by the head, and pushing alternately the right and left sides of the jaws forward, they press the body through their elastic gullet into the stomach, its outlines being visible for some time through the distended walls of the abdomen. Digestion is quick and much accelerated by the quantity of saliva which is secreted during the progress of deglutition, and in venomous snakes probably also by the chemical action of the poison. The primary function of the poison-apparatus in the economy of snakes is without doubt to serve as the means of procuring their food. But, like the weapons of other carnivorous animals, it has assumed the secondary function of an organ of defence. Only very few poisonous snakes (like Ophiophagus elaps) are known to resent the approach of man so much as to follow him on his retreat and to attack him. Others, as if conscious of their fearful power of inflicting injury, are much less inclined to avoid collision with man than innocuous kinds, and are excited by the slightest provocation to use that power in self-defence. They have thus become one of the greatest scourges to mankind, and Sir J. Fayrer has demonstrated that in India alone annually some 20,000 human beings perish from snake-bites. Therefore it will not be out of place to add here a few words on snake-poison and on the best means (ineffectual though they be in numerous cases) of counteracting its deleterious effects.

Chemistry has not yet succeeded in separating the active principle of snake-poison or in distinguishing between the secretions of different kinds of poisonous snakes; in fact it seems to be identical in all, and probably not different from the poison of scorpions and many Hymenoptera. The physiological effects of all these poisons on warm-blooded Vertebrates are identical, and vary only in degree, the smallest quantities of the poison producing a local irritation, whilst in serious cases the whole mass of the blood is poisoned in the course of some seconds or minutes, producing paralysis of the nerve-centres. That there is some difference, however, in the action of the poisons upon the blood has been shown by Fayrer, who found that the poison of Viperine snakes invariably destroys its coagulability, whilst nothing of the kind is observed in animals which perished from the bite of a Colubrine Venomous snake. The same observer has also experimentally demonstrated that the blood of a poisoned warm-blooded animal assumes poisonous properties, and, when injected, kills like the poison itself, although the bodies of the animals may be eaten by man with impunity. On the other hand, he has proved that the opinion generally adopted since Redi’s time, viz., that snake-poison is efficacious only through direct injection into the blood, is fallacious, and that it is readily absorbed through mucous and serous membranes, producing the same effects, though in a milder degree.

The degree of danger arising from a snake-bite to man depends in the first place on the quantity of poison injected: a large vigorous snake which has not bitten for some time is more to be feared than one of small size or one which is weakly or has exhausted its stock of poison by previous bites. The bite of some of the smaller Australian Diemenias and Hoplocephali is followed by no worse consequences than those arising from the sting of a wasp or a hornet, while immediately fatal cases are on record of persons bitten by the cobra or the large South-American Crotalines. In the second place it depends on the strength of the individual bitten: a man of strong physical constitution and energetic mental disposition is better able to survive the immediate effects of the bite than a child or a person wanting in courage. Thirdly, it depends on the position and depth of the bite: the bite may be merely a superficial scratch, or may penetrate into tissue having few blood-vessels, and thus be almost harmless; or it may be deep in vascular tissue or even penetrate a vein, producing immediate and fatal effects. It must be mentioned also that Fayrer is distinctly of opinion that the poison of some kinds is more powerful than that of others. The mere shock produced by the bite of a snake upon a nervous person may be sufficiently severe to be followed by symptoms of collapse, although no actual poisoning of the blood has taken place, or although the bite was that of an innocuous snake. It is said that persons have actually died under such circumstances from mere fright. The local appearances in the neighbourhood of a poisoned wound, which soon after the bite is much swollen and discoloured and very painful, readily prove its char acter; but this can be often ascer tained also immediately after the bite by the inspection of the wound,

—the teeth, which are so differently arranged in poisonous and non-

poisonous snakes, leaving a different pattern on the skin. As a non-

poisonous snake has four rows of teeth in the upper jaw, the pattern of its bite will more or less resemble fig. 4, whilst a poisonous snake leaves two rows of more distinctly marked punctured wounds in the place of the two outer series in the non-poisonous (see fig. 5). Of course, there may be modifications of these patterns, as, for instance, when one fang only hits or penetrates the part aimed at, or when the direction of the stroke is slanting, producing merely a scratch.

Unfortunately no antidote is known capable of counteracting or neutralizing the action of snake-poison. Some years ago injections of ammonia or liquor potassae were recommended, but there is the obvious objection that hardly in one out of a thousand cases of snake-bite would either the appliances or the operator be at hand. Fayrer’s experiments, however, have distinctly disproved the efficacy of this remedial measure. Equally useless is permanganate of potassium; it is indeed true that a solution of this compound destroys the properties of snake-poison when mixed with it; and therefore such of the poison as remains in the wound will be neutralized by the external application or injection of the permanganate, but the remedy is entirely without effect after the poison has passed into the circulation. Treatment is therefore limited to endeavours to prevent by mechanical means the poison from entering the circulation, or by chemical agencies to destroy or remove as much of it as possible that remains in the wound, and to save the patient from the subsequent mental and physical depression by the free use of stimulants. Whatever is or can be done must be done immediately, as a few seconds suffice to carry the poison into the whole vascular system, and the slightest delay diminishes the chances of the patient’s recovery. Courageous persons badly bitten...