148 OPHIDIA. 



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 fore- 

 most 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 im- 

 pression. 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 con- 

 cave 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 obhque aperture ; and the extremity 

 of the tooth is still more so, presenting the form 

 of a very narrow longitudinal groove. 



