84 A MANUAL OF DENTAL ANATOMY. 



which are to be met with (especially in the root) in large 

 numbers. 



Where they are numerous the vascular canals form loops, 

 so as to constitute a sort of plexus beneath the cementum. 



The Tapir, whose teeth in external configuration are not 

 very dissimilar to those of the Manatee, also has vascular 

 canals in the dentine ; a curious difference in this respect 



FIG. 43 ( a ). 





was pointed out by my father (Proc. Zoolog. Soc. 1851) 

 between the Indian and the American Tapir, the former 

 having the canals in the dentine of the crown of the teeth, 

 the latter having them not. The great extinct Megatherium 

 possessed dentine very rich in these canals : to the left of 

 the figure is seen the inner portion of the dentine, rich in 

 them in the middle a fine tubed dentine, forming the 

 external layer of the dentine of the whole tooth, and to the 

 right cementum, also rich in vascular tubes. 



In those teeth in which the whole pulp is converted into 

 solid material, and no pulp cavity remains, the last portions 

 of the pulp are often converted into dentine which has not 

 the same character as that of the rest of the tooth. Thus 



( l ) Dentine and cementum of Megatherium : the latter to the right of 

 the figure. 



