136 MAMMALIA ORDER VI.UNGULATA. 



of which differ from the Suina, and agree with one another in that the 

 molar teeth, instead of being simply tubercular, have the columns on their 

 crowns bent into the form of crescents, of which there are four in those of 

 the upper jaw. Technically, this type of tooth is known as the selenodont; and 

 all the animals possessing it are characterised by their power of ruminating, 

 or chewing the cud. Moreover, in all cases the third and fourth metatarsal 

 bones of the hind-feet are completely fused together to form a cannon-bone, 

 terminating inferiorly in two pulley-like surfaces, or trochleae, which carry 

 the two middle toes ; the same condition also obtaining in the corresponding 

 metacarpal bones of the fore-foot, except in one species of chevrotain. All 

 these animals are thus more specialised than the Suina ; the tubercular type 

 of molar, and the separate metacarpal and metatarsal bones of the foot, being 

 evidently the more primitive type. 



The first section of these selenodont Artiodactyles is known as the Tylopoda, 

 or cushion-footed group, and includes only the single family of the Camelidce, 

 now represented by the camels of the Old World and the llamas of South 

 America. Having selenodont molars and complete cannon-bones in both 

 feet, the camel tribe are specially distinguished by retaining incisor teeth in 

 the upper jaw, and by the lower canines being tusk-like and separated from 

 the incisors, which always form three pairs. The limbs are long, with the 

 thigh of the hinder pair less enclosed in the skin of the body than is the case 

 in the following families ; while the feet have but two toes, which are em- 

 bedded in a large pad-like cushion, and have only small nails on the upper 

 surface of their extremities. In the cannon-bones the two trochlese of 

 the lower extremity are widely divergent, and lack the median longitudinal 

 ridge found in all other members of the sub-order. The neck of these 

 animals is long and flexible, and its component vertebras present a peculi- 

 arity unknown in any other living Mammals. As regards their soft internal 

 parts, the camels have a less complex stomach than the true Ruminants ; 

 two of its chambers having special honeycomb-like cells for the retention of 

 water. 



From their allies the llamas, the two species of camel (Camelus) are readily 

 distinguished not only by their much larger bodily size, but likewise by the 

 presence of one or two fatty humps on the back, which diminish or increase 

 in size according to the physical condition of the animal. The head is large, 

 with relatively short and rounded ears ; the broad feet have the toes very 

 slightly separated ; the moderately long tail terminates in a tuft ; and the 

 nearly straight hair is not woolly. Adult camels have a total of 34 teeth, 

 with but one pair of upper incisors, although in the young there are three 

 pairs of the latter. The camels are among the few animals of which there 

 are now no wild representatives ; the so-called wild Bactrian camels of 

 Turkestan being now pretty conclusively proved to be the descendants of a 

 domestic race which escaped long ago from captivity. Of the two species, 

 the Arabian camel (0. dromedarius), which is found in a domesticated state 

 from Africa to India, is characterised by the single hump ; while in the stouter- 

 built and more shaggily-haired Bactrian camel (C. bactrianus) there are two 

 of these excrescences. The latter species is kept as a beast of burden from 

 the Crimea to Turkestan and Pekin, From the large loads they are capable 

 of carrying, as well as their power of enduring deprivation from water 

 for a considerable period, camels are invaluable as a means of transport in 

 dry countries, where the roads are not too rocky. They are, however, 

 best suited for traversing sandy deserts; but where the ground is wet, 



