Mr. Owen on the Toxodon Platensis, 205 



length by ninety in breadth. It was also perceived in the island of 

 Cyprus. 



April 1 9 — A paper was read, entitled " A description of the Cra- 

 nium of the Toxodon Platensis, a gigantic extinct mammiferous spe- 

 cies, referrible by its dentition to the Rodentia, but with affinities to 

 the Pachydermata and the Herbivorous Cetacea-," by Richard Owen, 

 Esq., F.R.S., Hunterian Professor of Anatomy to the Royal College 

 of Surgeons*. 



The author premises his anatomical description of the present 

 fossil, by an abstract from Mr. Darwin's account of the geological 

 structure of the district in which the cranium was found, from which 

 it appears that it was imbedded in a whitish argillaceous earth, 

 forming part of the banks of the Sarandis, a small stream entering 

 the Rio Negro, and about 120 miles distant to the north-west'of 

 Monte Video. 



The foundation of the whole surrounding country is granitic, but 

 covered, often to a considerable thickness, by a reddish argillaceous 

 soil, containing small calcareous concretions. 



The cranium in question equals in size that of the hippopotamus, 

 measuring two feet four inches in length, and one foot four inches in 

 extreme breadth. 



The form of the skull is elongate, depressed, and chiefly remark- 

 able for the strength and wide expanse of the zygomatic arches, 

 and the aspect of the occipital foramen and occipital region of the 

 skull, which slopes from below upwards and forwards. The maxillary 

 portion of the skull is compressed laterally, narrow, with large inter- 

 maxillary bones, slightly dilated at their extremity. 



The teeth consist of molars and incisors. The latter are four in 

 number in the upper jaw, the two middle ones very small, the two 

 external ones very large, curved, and with their sockets extending back- 

 wards in an arched direction, through the intermaxillary bones to the 

 maxillary, and terminating, without diminishing in size, immediately 

 anterior to the grinding teeth, where the large persistent pulps of 

 these incisors were lodged. In form and relative size these teeth 

 must have resembled the dentes scalprarii of the Rodentia. 



The molar teeth no less present a close approximation in their 

 form and structure to the molar teeth of the herbivorous rodents j as 

 is demonstrated in the detailed descriptions of one of these teeth found 

 by Mr. Darwin in another locality, but belonging to the same species 

 of Toxodon, and to an individual of the same size as that to which 

 the cranium here described belonged ; and of a portion of another 

 molar lodged in one of the sockets of the same cranium. The molar 

 teeth are seven in number on each side of the upper jaw, and from 

 the form of the sockets appear to have corresponded with each other 

 in structure. 



After this description of the teeth, the form, proportions, disposition 

 and connections of the different bones of the cranium are pointed out; 

 and the structure of the osseous cavities subservient to the organ of 



[* See our last volume, p. 404.] 



