356 A MANUAL OF DENTAL ANATOMY. 



and (in the upper jaw) downwards its track forms almost 

 the segment of a circle. Thus its anterior corner is the 

 first to come into use, at a time when the position of the 

 whole tooth is still exceedingly oblique, and the greater part 

 of it is still within the socket. 



The teeth as first formed consist of detached plates of 

 identinc coated with enamel, the tops of which are mammil- 

 lated ; these only coalesce after a considerable portion of 

 their depth has been formed, and that portion of the tooth 

 has been reached in which there is a common pulp cavity ; 

 here dentine is continuous from end to end of the tooth. 



Just as the cusps of a human molar are separate when 

 first calcified, so these exaggerated cusps or plates of an 

 elephant's tooth are separate from one another till a great 

 part of their length is completed, and they only coalesce 

 when they reach the level ef the common pulp chamber ; in 

 point of fact the elephant's tooth is mainly made up of its 

 cusps, the remaining portion being insignificant. 



Several of these detached plates, such as the one here 

 figured, are to be found at the back of the largest teeth 

 even at a time when the front corner has been erupted and 

 has come into wear. 



That the tooth is thus being built up only as it is required 

 is of obvious advantage to the animal in diminishing the 

 weight to be carried, and is also an economy of space. 



The teeth when they begin to be erupted do not at once 

 come into use over their whole surface, but they come for- 

 ward in an oblique position so that the front of the tooth 

 has been in use for some time, and its plates have been con- 

 siderably worn down, before the back of the tooth has 

 become exposed at all. Nay more, in the case of the larger 

 molars the front of the tooth is actually in use at a time 

 when its back is not yet completed. 



In the elephant there is no vertical succession of teeth 

 whatever; the manner of succession usual amongst mammals 



