584 UNGULATES. 



the teeth themselves, that the pulp was persistent, and that the growth 

 of these incisors, like those of the Rodentia, continued throughout 

 life. This condition, joined with the curvature of the socket, neces- 

 sarily implies a constant wearing away of the crown of the tooth, by 

 attrition against opposing incisors of a corresponding structure in the 

 lower jaw : and as a corollary, we infer that the teeth in question had 

 a partial coating of enamel, to produce a cutting edge, and were in 

 fact, true denies scalprarii. The number of incisors in the upper jaw 

 of Toxodon, — four, instead of two — is not without its parallel in the 

 Rodent order, the genus Lepus being characterized by a similar num- 

 ber of incisors, and of a similar relative size, but with a different 

 relative position, the small incisors in the Hare and Rabbit being so 

 placed immediately behind the large pair, as to receive the appulse of 

 the single pair of incisors in the lower jaw. Since the sockets of the 

 small mesial incisors of Toxodon gradually diminish in size as they 

 penetrate the intermaxillary bones, we may infer that, like ordinary 

 incisors, their growth was of limited duration, and their lodg- 

 ment in the jaw effected by a single conical fang. The lower 

 jaw of the Toxodon platensis, which was discovered at Bahia 

 Blanca, in latitude 39", on the east coast of South America, was 

 remarkably compressed or narrow from side to side ; while the 

 rami were of considerable depth, in order to give lodgment to the 

 matrices and bases of grinders enjoying uninterrupted growth. The 

 pulps of the six incisors of the lower jaw are arranged in a pretty 

 regular semicircle, whose convexity is downwards ; the teeth them- 

 selves are directed forwards and curved upwards like the inferior 

 incisors of the Rodentia. These incisors are nearly equal in size : 

 they are all hollow at their base, and the indurated mineral substance 

 impacted in their basal cavities well exhibits the form of the vascular 

 pulps which originally occupied them: they have, likewise, a' partial 

 investment of enamel ; but though, in this respect, as well as in 

 the curvature and perpetual growth, they resemble the ' dentes 

 scalprarii,' of the Rodentia, they differ in having a prismatic figure, 

 like the inferior incisors of the Sumatran Rhinoceros or the tusks 

 of the Boar. Two of the sides, viz., those forming the anterior 

 convex and mesial surfaces of the incisor, have a coating of 



