DtlNTITION. lo9 



the waved appearance presented by the enamel 

 on making sections of the teeth of these animals. 



The tusks of the elephant are composed of 

 ivory, and are formed precisely in the same 

 manner as the simple conical teeth already des- 

 cribed, excepting that there is no outer capsule, 

 and therefore no outer crust of enamel. The 

 whole of the substance of the tusk is constructed 

 by successive deposits of layers, having a conical 

 shape, from the pulp which occupies the axis of 

 the growing tusk ; just as happens in the forma- 

 tion of a univalve shell which is not turbinated, 

 as, for instance, the patella. Hence any foreign 

 substance, a bullet, for example, which may 

 happen to get within the cavity occupied by the 

 pulp, becomes, in process of time, encrusted 

 with ivory, and remains embedded in the solid 

 substance of the tusk. The pulp, as the growth 

 of the tusk advances, retires in proportion as its 

 place is occupied by the fresh deposits of ivory. 



The young animal requires teeth long before 

 it has attained its full stature ; and these teeth 

 must be formed of dimensions adapted to that of 

 the jaw, while it is yet of small size. But as the 

 jaw enlarges, and the teeth it contains admit not 

 of any corresponding increase, it becomes neces- 

 sary that they should be shed to make room for 

 others of larger dimensions, formed in a more 

 capacious mould. Provision is made for this 

 necessary change at a very early period of the 



