ELEPHAXTIDJ-: 



433 



moving succession does not require, or allow time for, their replace 

 merit by premolars. It must be noted, however, that, in the 

 Mastodon in some respects the least specialised in tooth-structure, 

 the .1/. americanus of North America, no vertical succession of the 



Fii.. ISO. — Restoration of the skeleton of Mastodon arvernensis, from the Pliocene of Europe. 



(After Sismonda.) 



molars has yet been observed, although vast numbers of specimens 

 have been examined. 



The Mastodons have fewer ridges on their molar teeth than 

 the Elephants ; the ridges are also less elevated, wider apart, have 

 a thicker enamel-cover- 

 ing, and scarcely any 

 cement filling up the 

 -pace between them. 

 Sometimes (as in M. 

 americanus) the ridges 

 are simple transverse 

 wedge - shaped eleva- 

 tions, with straight or 



concave edges. 



In 



Fig. 187.— Oblique side and crown view of the last upper 

 molar of Mastodon arvernensis. (From Owen.) 



other species the sum- 

 mits of the ridges are 

 more or less subdivided into conical cusps, and may have accessory 

 cusps clustering around them (as in M. arvernensis, see Fig. 187). 

 Y\ hen the apices of these are worn by mastication, their surfaces 

 present circles of dentine, surrounded by a border of enamel, and 

 as the attrition proceeds different patterns are produced by the 

 union of the bases of the cusps, a trilobed or trefoil form being 

 characteristic of some species (Fig. 188). 



28 



