168 



HIGH SCHOOL ZOOLOGY. 



principle referred to above. They tlius contrast witli the 

 IJngiiiciilata, which retain for the most part tlie ty[)ical nuniher 

 of toes. If we, however, extend our survey from the living to 

 the fossil Ungulates, we shall find that the reduction of the 

 )iumber of toes is comparatively recent in the histoiy of their 

 series, the oldest forms being five-toed like most Unguiculata, 



24. The most primitive order of the hoofed animals in this res- 

 l)ect (Fig. 110 E) is that of thg Proboscidea or Elephants, al- 

 though in other respects it is one of the most specialised and high- 

 ly organised of the sei'ies. The only living genus is Elephas, 

 represented by two species E. indicus and africanus, the latter 

 distinguished from the former by its enormous ears, and by the 

 lozenge-shaped ridges on the molar teeth. In both the living 

 forms, the thick skin has only a few isolated bristles, but the 

 fossil mammoth {E. 2^'''i^nigenius), which was abundant in 



Fig. 114 — Skeleton of Mastodon. 



Siberia and Alaska, and of which frozen carcases have been 

 found, was covered with wool intermingled with coarse hair. 

 Most of the peculiarities of the skull are attributable to the 

 singular dentition of the Elephant, which consists of two huge 

 incisor tusks in the premaxillaries and, in addition, six grinders 



