282 BRITISH MAMMALS 



reached the four-fingered stage are well illustrated at the present 

 day by the hippopotamus, the swine, and those curious little 

 creatures, the tragulines,^ which represent the parent stock of 

 the modern Ruminants. Outside these groups such creatures as 

 deer, oxen, sheep, antelopes, giraffes (Pecora), and camels have 

 entirely, or to a great extent, lost the bones of the outer toes, 

 though in some cases they still retain fragments of these ; and, 

 except in the giraffes and a few antelopes and in the camels, the 

 missing toes are still represented by what are called the false hoofs, 

 so that at first sight an ox, a sheep, or a deer appears to be four-toed. 

 Not only in the course of evolution did the higher Artiodactyles 

 reduce their functional toes to a pair, but the first bones of those 

 toes (which are called the metacarpals and metatarsals ^) gradually 

 fused into a single bone (called the cannon bone), down the 

 middle of which a slight groove indicates in some forms the 

 original duplicate character of the bone. 



The Artiodactyles also show considerable modifications in 

 their teeth, as they differentiate from the main stock In the 

 hippopotamus and the pig the teeth are of a more generalised 

 character. There are in most swine, and in the earlier types of 

 hippopotamus, the full number of six incisors above and six below. 

 Canines are likewise present in both jaws, and there are generally 

 four pairs of premolars and three of molars in each jaw. More- 

 over, in the swine and in the hippopotamus the molar teeth are 

 short in the crowns, and their surface is divided into a number 

 of nipple-like mounds, originally four in number in each tooth. 

 These two groups also, together with many extinct allied families, 

 exhibit no tendency whatever to the growth of bony, horn- 

 bearing projections from the skull. 



In the more modern types of Artiodactyles, represented by 

 the camels,^ tragulines, and horn- or antler-bearing Pecora, the 

 incisors in the upper jaw are either reduced to one on either 



* Pygmy musks, chevrotains. 



^ These metacarpals (for instance) are the five bo.nes bound up in the 

 palms of our hands. 



' Which, however, are quite an independent development. 



