127 



The surface of the supra-orbital process of the frontal bone is deserving 

 of attention : as it presents a peculiar ruggedness which is not found in 

 any other part of the skull, the irregularity seems, as it were, to have 

 been produced by the impression of numerous small tortuous and ana- 

 stomosing vessels. In the skull of a Sumatran two-horned Rhinoceros 

 in the Museum of the College (No. 816), the circumference of that part 

 of the surface of the skull which supported the posterior horn, and which 

 includes precisely the same part of the os frontis, presents the same 

 character, the surface bein^ broken by numerous vascular impressions. 

 On the supposition that this character of the supra orbitary arch in the 

 Toxodon might indicate the superincumbency of a bony case, I examined 

 the skulls of two Armadillos, Dasypus Peha and Das. sex-cinctus, 

 and found that in the Dasypus sex-cinctus, the supra-orbital ridges, 

 which are slightly elevated to support the cephalic plate, presented, in a 

 minor degree, a corresponding rugosity. It may be conjectured, there- 

 fore, either that the Toxodon was defended by an ossified integument 

 like the Armadillo, or that it was armed with an epidermic production 

 analogous to the horn of the Rhinoceros ; ur that the rugous surface 

 in question had as little relation with the parts that covered it, as the 

 sculptured surface of the malar bones in the Cavy. 



The cavity of the nose is extensive, and the remains of the ossa spon- 

 giosa superiora testify that the Toxodon enjoyed the sense of smell to a 

 degree equal at least to that of the Hippopotamus. 



The superior maxillary bones are united posteriorly to the malar, they 

 ascend and join the frontal and nasal bones, their outer surface is 

 almost vertical, is smooth, and slightly undulating, is perforated at its 

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

 intermaxillaries by a suture running in the sigmoid direction 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 im- 

 portant difference between the Toxodon and Hippopotamus. The chief 

 peculiarity in the maxillary bones obtains in the arched form of the alveolar 

 processes, corresponding with the shape and position of the grinders 



