292 TEETH OF THE MEGATHERIUM. 



of the most efRcient arrangement for the finer comminu- 

 tion of the food, at the part of the mouth which is nearest 

 the fauces. 



In the tusks of the Mastodon giganteus^ the outer layer 

 of cement is rehxtively thicker than in the tusks of the 

 mammoth, or in those of the Indian elephant. The ge- 

 neral character of the microscopic structure of the ivory 

 of the mastodon's tusk is the same as that of the ele- 

 phant. 



By the minuteness and close arrangement of the den- 

 tinal tubes, and especially by their strongly undulating 

 secondary curves, a tougher and more elastic tissue is 

 produced than results from their disposition in ordinary 

 dentine; and the modification which distinguishes "ivory" 

 is doubtless essential to the due degree of coherence of so 

 large a mass as the elephant's tusk, projecting so far from 

 the supporting socket; and to be frequently applied in 

 dealing hard blows and thrusts. 



TEETH OF THE MEGATHERIUM. 



The megatherium (Gr. megas^ great ; thenon, beast), so 

 called from its colossal size — being as large as the 

 elephant, and even surpassing that hugest of existing 

 quadrupeds in some of its proportions — was once an in- 

 habitant, and apparently in some numbers, of the Ameri- 

 can continent, especially its southern division, and sub- 

 sisted on a similar kind of food to the elephants, viz : the 

 smaller branches and leaves of trees ; but all the genera 

 and species of megatheroid beasts are now extinct. 

 Nevertheless, from the fossil remains of the megatherium 

 the anatomist is able unerringly to deduce the nature of 



