124 



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 dentes scalprarii. 

 The numher 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 number 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. 



As the sockets of the small mesial incisors of Toxodon gradually di- 

 minish in size as they penetrate the intermaxillary bones, we may infer 

 that the pulp was gradually absorbed in the progress of their develop- 

 ment ; and that, like ordinary incisors, their growth was of limited dura- 

 tion, and their lodgement in the jaw effected by a single conical fang. 



The orbit of the Toxodon forms the anterior boundary of the zygo- 

 matic area ; it is about as distinctly defined as in the Tapir or Dugong, 

 having its osseous rim less complete than in the Hippopotamus, yet more 

 developed than in the Capybara, Coypus, and many other Rodents, in 

 which the orbit is scarcely distinguishable in the cranium from the small 

 space occupied by the origin of the temporal muscle. The lower boun- 

 dary of the orbit in the Toxodon is formed by an excavation in the 

 upper and anterior part of the zygoma; the upper boundary by a strong 

 and rugged overarching process of the frontal bone, the posterior angle 

 of which descends a little way, but leaves a space of three inches and a 

 half between it and the opposite angle of the malar bone below, the cir- 

 cumference of ihe orbit being completed probably by ligament in the 

 recent subject. The cavity thus circumscribed is remarkable for the 

 preponderance of the vertical over the transverse or longitudinal diameter, 

 and indicates great extent of motion of the eyeball in the vertical direc- 

 tion, such as may be supposed to be well adapted to the exigencies of an 

 amphibious quadruped. The orbit of the Capybara, or Water Hog, 

 makes a near approach to the form just described. In the elevation of 

 the supra-orbital boundary, and its outward projection, in the Toxodon, 

 we perceive an approximation to the form of the orbit in the Hippopo- 



