270 



ZOOLOGY. 



there existed forms wliich indicate that the Proboscidians 

 and Ungulates had a common origin. In the elephants 

 the upper incisor teeth are enormously developed, forming 

 the tusks so characteristic of these animals, while there are 

 none in the lower jaw. There are no canine teeth, wliile 

 the few molars are large and transversely ridged. In the 

 elephants the ridges on the molar teeth are numerous, the 



Fig. 307. — Section of an elephnnt's skull, showing: the small size of the brain 

 cavity as compaj-ed to the whole skull, anil the minierous large air-cells. 

 V, po.sterior nostrils; 1.3. cavity of the nose; a. front opening of the bony nos- 

 trils, to the edge of which the trunk is attached. 



spaces Ijetween tliem being filled with cement. The young 

 mastodon has cement on the u]iper surface of Ihe tooth; 

 the ridges afterwards become free and covei'cd with enamel. 

 A peculiarity in the elephant's sInuII is its large size, the 

 brain cavity being very small in pro])ortion to the bulk of 

 the skull itself. To give lightness to wliat would be other- 

 wiee an insu2>portable weight, the cranial bones contain 



