112 Vertebrata. 



exceedingly small objects. The teeth of an elephant 

 consist of two tusks or incisors in the upper jaw, 

 which grow continuously, sometimes to enormous 

 sizes, and furnish the ivory of commerce. There are 

 no incisors in the lower jaw, but there are on each 

 side of each jaw two large, rough-crowned, quadrate 

 teeth, whose crowns are marked by transverse enamel 

 ridges, used in grinding the twigs and shoots of trees 

 on which these animals feed. There is a constant 

 succession of these molars, seven of which are de- 

 veloped during the life of the animal on each side of 

 each jaw, but never more than two, or at most three, 

 are laterally functional at one time. The skull is 

 enormous, most of its bulk consisting of huge air- 

 cells, and the brain is large and convoluted on the 

 surface. Two species of elephants are now living, 

 confined to the tropics : one in Africa, known by its 

 convex forehead and flapping ears ; one in India, 

 which has a concave forehead and smaller ears. 

 Formerly several species of elephants lived in Europe, 

 and remains of one form have been abundantly met 

 with in some parts of the British Islands. In Siberia, 

 also, there exist numerous remains of a hair-clad ele- 

 phant, the mammoth, which had probably existed 

 down to a comparatively modern time. 



