but is suspended at the end of a long slender bone, which is attached to the hinder-part of the skull by muscles and ligaments so as to be very moveable. It will be readily seen how this contrivance permits a very wide expansion of the posterior part of the lower jaw, which is attained

SKULL OF SNAKE.

in a less degree in front by the nature of the union of the two branches, they not being soldered together there as usual, but simply tied by ligaments. Other bones of the skull have a correspondent freedom.

Both pairs of jaws, for the most part, are set with numerous slender acute teeth, having a double curve, and pointing backwards: the bones of the palate also are furnished with similar teeth, so that there are four nearly equal rows of teeth in the upper part of the mouth, and two in the lower. The mode of swallowing prey is as follows:-Some of the front teeth being struck into the victim, one side of the lower jaw is thrust forward as far as the ligaments will allow, when the teeth of that side take a fresh hold, which is retained, while the other side of the jaw performs a corresponding movement; thus by the alternate advance of the two sides of the jaw, which their excessive mobility admits, and by the backward inclination of the teeth allowing the food to move much more readily in one direction than another, this is gradually drawn into the throat, forcing asunder, and dislocating, as it

were, all the bones of the mouth, as it proceeds, until at length it is deposited in the elastic and expansible gullet.

În many of the species, the teeth of the upper jaw manifest a tendency to increase in size above those of the palate, and to decrease in number. The Water-serpents have but few, but the foremost one is larger than those which succeed it, and is hollowed in a peculiar manner, so as to form a curved and pointed tube, connected with a gland that secretes a poisonous fluid. At length in the most venomous of the whole Order, the upper jawbone is reduced to a small size, carrying a single curved and tubular tooth of great length, which is followed only by others of the same structure, undeveloped, and destined to replace it after its loss by decay or violence.

It is common to represent the poison-fang of a Serpent as simply tubular, or pierced through its centre; this, however, conveys a wrong impression. The substance of the tooth is not pierced at all. Let us suppose the simple tooth of a Boa, or of a common Snake, to be flattened transversely, and its edges then to be bent round until they meet, and to be soldered together, so as to form a tube open at each end. Such is the fang of the Viper, the line by which the edges unite running down the front of the tooth, where it is convex; while the posterior or concave side is that which contains the pulp-cavity or true centre, considered structurally. The union of the edges is incomplete towards the gum, forming an oblique aperture; and the extremity of the tooth is still more so, presenting the form of a very narrow longitudinal groove.

The tube thus formed communicates with the poison-bag, into which the deadly fluid is poured from glands which lie on each side of the head beneath the eye. Each consists of a number of long narrow lobes, extending from the main duct which runs along the lower border of the gland upwards and slightly backwards. Each lobe gives off smaller lobes from its sides, and each of these is subdivided into smaller secreting sacs; and the whole gland is surrounded by a membrane connected with the muscles, by whose

contraction the several lobes are pressed and emptied of the poison. This fluid is then conveyed through the duct to the poison-bag. "We may suppose," says Professor Müller, "that as the analogous lachrymal and salivary glands in other animals are most active during particular emotions, so the rage which stimulates the venomsnake to use its deadly weapon must be accompanied with an increased secretion and great distention of the poison-glands; and as the action of the compressing muscles is contemporaneous

with the blow by which the Serpent inflicts its wound, the poison is at the same moment injected with force into the wound from the tip of the perforated fang."

A singular exception to the general structure of the teeth occurs in a South African Snake (Deirodon, OWEN), described by Dr. Andrew Smith, which is so interesting that we quote Professor Owen's description of the dentition and its use. The teeth are so small as to be scarcely perceptible; and are besides so soon liable to be lost, that the reptile has been described as toothless. The office assigned to this Serpent is to keep down the inordinate increase of the smaller birds, by preying on their eggs; and, as has been observed, the apparent defect in its dentition is in reality one of those beautiful instances of adaptation of structure to the exigencies of the case, to which every naturalist has so often to advert. "If," says Professor Owen, "the teeth had existed of the ordinary form and proportion, in the maxillary and palatal regions, the egg would have been broken as soon as it was seized, and much of its nutritious contents would have escaped from the lipless mouth of the Snake in the act of deglutition; but, owing to the almost edentulous state of the jaws, the egg glides along the expanded opening unbroken, and it is not until it has reached the gullet, and the closed mouth prevents any escape of the nutritious matter, that the shell is exposed to instruments adapted for its perforation. These instruments consist of the inferior spinous processes of the seven or eight posterior cervical vertebræ, the extremities of which are capped by a layer

of hard cement, and penetrate the dorsal (upper) parietes of the oesophagus: they may be readily seen even in very young subjects, and in the interior of that tube, in which their points are directed backwards. The shell being sawed open longitudinally by these vertebral teeth, the egg is crushed by the contractions of the gullet, and is carried to the stomach, where the shell is no doubt soon dissolved by the gastric juice."*

The tongue in this Order is slender, and divided into two long and pointed filaments, which are capable of being entirely retracted within a sheath, or of being protruded from the mouth, with great swiftness of motion. Serpents are said to be enabled to lap up fluids with this forked tongue, which, however, seems to be ill suited for such an operation. The vulgar notion which associates a hurtful power with the tongue, often spoken of as the "sting," is entirely er

roneous.

The mode in which respiration is performed is described by MM. Duméril and Bibron to be as follows:-"The glottis, which has two lips, and represents a very simple larynx, opens in the mouth beneath the sheath of the tongue; by means of the muscles of the os hyoïdes [or bone of the tongue], which push it, it is raised so as to be presented in a dilated state behind the back nostrils. The vacuum caused by the action of the ribs in the belly tends to dilate the lung, which through the medium of the trachea, immediately admits the air which is introduced during an inspiration: this is slow, continuing for some * Odontography.

+ Our European Snakes drink by suction, not by lapping.