HIGH SCHOOL ZOOLOGY. 169 



on each side in each jaw, wlij^h, howevei-, instead of being pre- 

 sent simultaneoiisly, succeed each other, so that only one, or at 

 most two of the six are in function at the same time. The length 

 of the tusk-sockets causes the great height of the skull, which 

 is especially large in the Indian elephant, not so much from the 

 size of the brain, as from the great thickness of the middle or 

 spongy layer of the cranial bones. In the fossil genius Mastodon, 

 (Fig. 114) of which many remains are found throughout Ontai-io, 

 there were tusks in the lower jaw as well ; the grinders suc- 

 ceeded each other as in the elephant, but they had from three to 

 six transverse rows of tubercles, from which the genus derives its 

 name. One can arrive at the structure of the elephant's tooth 

 from that of the mastodon, by imagining the transverse rows 

 added to in numbei', their surfaces worn do^vn and the intervals 

 between them filled up with cement. ^ 



The neck is so short that the proboscis or trunk, an elongated 

 external nose with a finger-like pi-ocess at its tip over the nostrils, 

 becomes necessary for securing food ; it requii-es, thei-efore, to be 

 very muscular and sensitive. The apparent disproportion between 

 the length of the jbreand hind limbs is due to the fact that the 

 latter are inclosed within the skiii of the loins nearly to the 

 knee-joint, but the bones of the fore and hind legs are ap- 

 proximately of the same length. A curious difference of gait 

 is observable between the elephant and higher Ungulates on 

 account of the position of the elbow and knee joints in the former; 

 they occupy the middle of the limbs, the metapodials being 

 quite short and contributing to, tbe_ formation of the soles of 

 the feet, whereas in the latter, the metapodials become the 

 long cannon bones, the wrist and ankle joints^'are raised to 

 the~imddle of the limbs, being known as the " kne^ " and 

 " hock^" respectively, and the true elbow and knee joints are 

 close tip to the trunk. The higher Ungulates therefore are not 

 plantigrade like the elephants, Taut walk on the tips of the 



distal joints of the digits. (Fig. 1 1 0, P and 0). 

 12 



