THE HOOFED MAMMALS. 133 



form, although it ■was generally of rather larger size. This difference in size 

 was once thought to indicate that tlie fossil form was a distinct species, but 

 the discovery of a half-fossilised jaw in the alluvium of the Nile near 

 Kalabshi, in Nubia, showed that in former times the African liippopotamus 

 attained dimensions as large as the European form. In England the hippo- 

 potamus ranged at least as far north as Leeds, and it is a remarkable 

 circumstance that in many places its remains have been found in association 

 with those of the reindeer. In Algeria, where the genus is now unrepre- 

 sented, a small species (H. hipponensis) flourished during the Pleistocene 

 period ; this being distinguished by having three pairs of lower incisor teeth, 

 which differed from those of other members of the genus in having their 

 enamel smooth and their extremities somewhat expanded, thus approximat- 

 ing to the corresponding teeth of the pigs. Equally noteworthy is the 

 occurrence of another species {H. lemerUi) in Madagascar, where its remains 

 are common in the great marsh of Ambulisatra. Somewhat interniediate 

 between the common and the Siwalik species, this rather small hippopotamus 

 had sometimes three and sometimes two pairs of incisors in the lower jaw. 

 One or two small species, which may have been partially terrestrial in their 

 habits, dwelt in Italy, Malta, and some of the other Mediterranean islands 

 in past times. 



From the hippopotami the members of the great pig tribe, all of which 

 are confined to the Old World, are at once distinguished, not only by their 

 lighter build and longer limbs, but likewise by the peculiar 

 form of the snout, which always terminates in an oval, fleshy The Pig Tribe. 



disc, in which are perforated the nostrils. The feet, al Tamily Suidai. 



though severally furnished with four toes, are also different 

 in that they are much narrower, and that the middle pair, which are alone 

 functional when the animals are walking on firm ground, are much larger 

 than the lateral ones, and have flat adjacent surfaces, so as to form a 

 so-called divided hoof. In the teeth, the incisors, which are somewhat vari- 

 able in number, are rooted, and thus only grow for a brief period, while the 

 canines are rootless, and distinguished by the upper pair being directed more 

 or less markedly outwards or upwards. The molar teeth, which are tuber- 

 culated, do not wear into the distinct trefoils characterising the correspond- 

 ing teeth of the hippopotami. 



The true pigs [Sus) differ from all the other members of the family in 

 having the typical number of 44 teeth, although in certain African represen- 

 tatives of the genus the anterior premolars are frequently shed in the adult. 

 The canines of the upper jaw are curved outwards and upwards, and in the 

 males are very large, and project far beyond the lips; they are worn on their 

 outer convex surfaces to a sharp edge by the attrition of the longer and more 

 slender lower tusks. In the upper incisors, which are directed downwards, 

 the first is considerably larger than the second, which, in turn, succeeds the 

 third in size ; and the three pairs of lower incisors are directed almost 

 horizontally forwards. The skull is characterised by tha great elevation of 

 its hinder or occipital portion. The external form of the pigs is too well 

 known to need anything in the way of description ; but it may be remarked 

 that whereas in many of the domesticated breeds the skin is nearly naked, in 

 the wild boar it is covered with a thick coat of bristly hair. "Whereas the 

 adults of all the species are more or less uniformly coloured, the young of 

 the wild breeds are longitudinally striped and spotted with yellow or white. 

 The typical representative of the genus is the wild boar (S. scro/a)^ of Europe, 



