630 



To these osteological and dental characters may be added some important modifications of internal 

 structure, as e. g. the complex form of the stomach in the Hippopotamus, Peccari, and Ruminants, the 

 comparatively small and simple caecum, and the spirally folded colon, which equally indicate the mutual 

 affinities of the even-toed or Artiodactyle hoofed quadrupeds and their claims to be regarded as a natural 

 group of the Ungulata. Many extinct genera, e. g. Choeropotamus, Anthracotherium, Hyopotamus, 

 Dichodon, Merycopotamus, Xiphodon, Dichobune, Anoplotherium, have been discovered, which once 

 linked together the now broken series of Artiodactyla, represented by the existing genera Hippopota- 

 mus, Sus, Dicotyles, Camelus, Moschus, Camelopardalis, Cervus, Antilope, Ovis, and Bos*. 



Order CARNIVORA. 



Family Phocida (Walrus, Seals). 

 Genus Trichecm. 



Dental formula : i ~ 2> c^,m <-Ei=28. 



3860. The skeleton of the Walrus (Trichecm Rosmarm}. 



The vertebral formula is: 7 cervical, 14 dorsal, 6 lumbar, 3 sacral, and 9 caudal. The 

 last cervical has the transverse processes imperforate. Nine pairs of ribs directly join the 

 sternum, which consists of eight bones. The os penis is attached to this skeleton. The 

 young Walrus has three teeth in each premaxillary bone and two on each side of the fore part 

 of the mandible : they soon disappear, except the outer pair of upper incisors, which remain 

 close to the maxillo-premaxillary suture, on the inner side of the long canine tusks, and by 

 their thick obtuse form seem to commence the series of small and simple molars. In the 

 adult there are usually three molars on each side, behind the permanent molariform incisor, 

 and there are four similar teeth on each side of the lower jaw, the anterior one passing into 

 the interspace between the upper incisor and first molar, and therefore being the homotype 

 of that molar. A fourth upper molar (or fifth, counting from and including the molariform 

 incisor) is occasionally present in the young Walrus, and the dental formula as given above 

 will derive illustrations from the descriptions of the following crania : they do not, however, 

 afford the means of distinguishing the teeth called ' molar ' into ' premolars ' and ' true 

 molars,' and the molariform tooth in the premaxillary bone will be included in the series of 

 molars, as enumerated in the succeeding descriptions. 



The food of the Walrus consists of sea-weed and bivalves : the molars are well adapted to 

 break and crush shells ; fragments of a species of My a have been found, with pounded sea- 



* For a further illustration of the affinities of the Ungulata the reader is referred to the " Descrip- 

 tion of two extinct Anthracotherioid Animals," by Prof. Owen, in the ' Quarterly Journal of the 

 logical Society,' November 1847. 



