Page:Natural History, Reptiles.djvu/156

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

In 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.