FOSSIL MAMMALIA- 



27 



and resembles the Armadillos among the Edentata ; excepting that the post- 

 dental part of the bony palate in the Toxodon is suddenly contracted in breadth. 

 The palato-maxillary suture is in the form of a chevron, with the angle directed 

 forwards, as in the Hippopotamus and Capybara, but truncated. 



The superior maxillary bones (f, PL II.) are united posteriorly to the malar, as 

 above described : they ascend and join the frontal and nasal bones : their outer sur- 

 face is almost vertical, smooth, and slightly undulating ; perforated at its posterior 

 part by the ant-orbital foramen, and joined anteriorly to the intermaxillaries by a 

 suture running in the sigmoid direction (as shewn in PL II.) from the middle of the 

 nasal cavity, to within four inches of the anterior boundary of the upper jaw. 

 We have, in the position and extent of this suture, and the absence of tusks and 

 their large prominent sockets, a most important difference between the Toxodon and 

 Hippopotamus. The chief peculiarity in the maxillary bones, obtains in the 

 arched form of the alveolar processes, corresponding to the shape and position of 

 the grinders above described, and which are peculiar among known mammalia to 

 the present genus. The palatal surface of the maxillary bones is obliquely perfo- 

 rated by two large foramina, from which two deep longitudinal grooves extend 

 forwards, and are gradually lost ; we find the posterior palatine foramina repre- 

 sented by similar grooves and foramina in the Capybara. 



The intermaxillary bones (d, Pis. II. and III.), though large, are relatively of 

 less extent than in the Rodents generally. The nasal processes do not reach the 

 frontal bone, but are limited to the anterior half of the nasal boundary; approaching 

 in this respect to the Herbivorous Cetacea. In the outward expansion of their 

 anterior extremities, the intermaxillaries resemble those of the Hippopotamus, in 

 which, however, this character is more strongly marked. The intermaxil- 

 laries in the Hippopotamus are also much less firmly united to the maxillary 

 bones than in the Toxodon, and are consequently commonly lost in the fossil 

 crania. On the palatal surface of the intermaxillary bones there are two grooves 

 which diverge forwards from the line of the suture ; and anteriorly to these grooves 

 there are the two large anterior palatine foramina. The maxillo-intermaxillary 

 sutures on the palate converge as they extend backwards to a point ; there appears 

 to have been a fissure left between this suture and the mesial suture of the inter- 

 maxillaries ; in which structure the Toxodon resembles the Hippopotamus. 



After summing up the different affinities, or indications of affinity, which are 

 deducible from the cranium of this most curious and interesting fossil mammal, 

 we are led to the conclusion, assuming it to have had extremities cased in hoofs, 

 that it is referrible to the Order Pachydermata. But the structure, form, and 

 kind of teeth in the upper jaw, prove, indisputably, that the gigantic Toxodon 

 was intimately related to the Rodent Order. From the characters of this order, 

 as afforded by the existing species, the Toxodon, however, differs in the relative 



