^88 MAMMALS, PHYLUM CHORDATA 



can be traced back to the ancient insectivores. Although, with 

 one or two exceptions, all modern Carnivora are carnivorous, 

 they exercise the habit in different ways ; there are therefore 

 several different radiations within the main line, and it is difficult 

 to choose a typical animal for description. The dog (Cams 

 familiaris) may, however, be taken as a central example, more 

 carnivorous than the bears but less so than the cats. Its skull 

 has already been described (pp. 425-33) and shows the typical 

 large canine, small incisors and cutting (sectorial) cheek teeth, 

 with the highly developed carnassials ; the roller articulation 

 of the jaw, preventing lateral motion, is also noteworthy. Other 

 features of the skeleton are the raising of the feet, so that the 

 animal is digitigrade and walks on the distal phalanges, and the 

 absence of the clavicles. The limbs, like the jaws, have Httle 

 lateral motion. The brain is relatively large, and hearing and smell 

 are good ; sight, however, is by human standards poor, though 

 probably at least as good as in most mammals. Primitive mam- 

 malian features are the separate forearm and shin bones, the 

 presence of five toes on the fore-limb and four on the hind, 

 and a bicornuate (that is, forked) uterus. The stomach is simple 

 and the caecum small. 



The origin of the domestic dog is unknown, but fossil remains 

 suggest that he was an early companion of man. The wolf {Cams 

 lupus) was abundant in Britain in the Middle Ages, but became 

 extinct in England about the end of the fifteenth century, and 

 in Scotland in the eighteenth. The fox [Vulpes viilpes), which 

 is similar in general structure to the dog, is common over most of 

 Britain, but owes its survival, at least in the lowlands, to protection. 



The cats (family Felidae) are more strictly carnivorous than the 

 dogs, which feed largely on carrion and sometimes take vegetable 



matter. They have smaller incisors, fewer and sharper cheek teeth, 



3 I 3 I 

 relatively longer canines (dental formula ), and the claws 



are sharper and are normally held retracted into sockets so that 

 they do not touch the ground. This feature, as well as the presence 

 of a small clavicle, may be connected with the frequent arboreal 

 habit. Besides the domestic Felis catus, which probably originated 

 in Egypt and is perhaps a hybrid, there is in Britain the wild cat 

 [F. silvestris), now confined to the Highlands of Scotland. Its food 

 consists of relatively large animals, such as grouse and blue hares. 

 At the other extreme are the bears (Ursidae), which are 



