THE TEETH OF REPTILES. 253 



The dentine is continued down to a very fine point, and 

 it is cased by an exceedingly thin layer of enamel, not 

 much more than ^-^ of an inch in thickness in our common 

 English viper : thus the utmost sharpness is secured, 

 without loss of elasticity, which would have ensued had 

 its point been made up of brittle enamel only. Enamel 

 covers the whole exterior of the tooth but does not extend 

 into the poison canal in the viperine snakes ; in Hydrophis 

 I believe that it does. As the point is simple, the tooth 

 germ of a poison-fang only becomes distinguishable from 

 that of another ophidian tooth after the tip of the tooth has 

 been formed, when a groove appears in its side (see 8 and 9, 

 in Fig. 108). 



It being the habit of poisonous snakes to make use of 

 these weapons to kill their prey, which they consequently 

 do not swallow alive, it would obviously subject them to 

 no little inconvenience to be without these weapons for 

 any considerable length of time, while from their habit of 

 striking living prey the long fangs must be very liable to 

 being broken off by the jumping away of the creature struck, 

 to say nothing of the great force with which the blow is 

 given. 



In the most typical (viperine) poisonous snakes the 

 succession of teeth is conducted upon a plan which is 

 unique, and which is excellently adapted to save loss of 

 time in the replacement of a lost poison fang. Upon the 

 movable maxillary bones there is space enough for two 

 poison fangs, side by side ; only one, however, is fully 

 anchylosed to the bone at a time, and occupies a place to 

 the extreme right or extreme left of the bone, leaving vacant 

 space for another by its side. 



When the tooth in use falls, it will be succeeded by a 

 tooth upon the vacant spot by its side, not upon the spot 

 upon which itself stood, so that the places on the right 

 and the left of the bone are occupied alternately by the tooth 



