ELEPHANT AND MASTODON. 71 



the dimensions being about seven inches in length, by four of 

 width at tjie anterior end. The height of the crown, from the 

 base of the enamel to the summit of the first ridge {vide 

 Section, PL VII. fig. 2, or PI. III. fig. 9, P.A.S.), is about 

 two and a half inches, decreasing a little successively to 

 the fourth or last principal ridge. The grinding surface is 

 divided in two directions, viz. longitudinally along the axis 

 by a narrow cleft, which, as in the hippopotamus and most 

 other pachydermata, bisects it into nearly equal segments ; 

 and transversely by four deep open hollows, alternating 

 with as many trenchant ridges. Each of the lateral divisions 

 of these ridges is composed of a pair of compressed con- 

 fluent points ; in the upper molars, the outer division is 

 more elevated and slopes gradually towards the inner side, 

 which, although lower, is the most complex in composition, 

 giving off the ' talons ' and accessory tubercles, which are 

 more or less developed in different species, the inner 

 point being commonly the largest. This relation continues 

 during the wear of the teeth, the inner side being more 

 worn by the process of trituration than the outer. The 

 teeth of the lower jaw agree with the upper in the form and 

 subdivision of the crown ; but the disposition of the lateral 

 segments is reversed, the inner being higher, and continuing 

 so during the wear, while the outer are lower, but more com- 

 plex in composition. The higher and lower portions of the 

 crowns of the opposed teeth are thus brought to act against 

 each other, and serve more effectually the triturating function 

 of the teeth. The plane of the grinding surface is nearly 

 level from back to front, both in the upper and inferior 

 grinders. In consequence of the peculiar mode of protrusion 

 of the teeth from behmd forwards, the crown ridges come 

 successively into use, commencing with the first, and each of 

 the lateral divisions is ground down to a rhomboidal disc, 

 surrounded by a band of thick enamel : as the wear of the 

 tooth advances, the separate discs unite, forming a wide 

 transverse depression corresponding to the configuration of 

 the ivory nucleus, and the shell of enamel which invests it. 

 The ' cement,' or third dental substance, is very sparingly 

 developed upon the crovnis of the molars of the North Ame- 

 rican mastodon, being only distinguishable in a thin layer 

 under the microscope. It is more abundant upon the fangs. 

 The anterior ridge is supported by two stout united fangs, 

 and the three posterior ridges by fangs agreeing with them in 

 number, but more or less confluent into an irregular hollow cone. 

 In the existing Indian elephant, the last grinder of the 

 upper jaw is of a subtriangular rhomboidal form in the vertical 

 section, widely different from that of the North American 



