MAMMALS^ 401 



large, uterus bicornuate ; placenta zonary, non-deciduate ; mammae pectoral, 

 two in number. 



The elephants and their extinct relatives form a most interestino- group, 

 highly dififerentiated in some respects, more generalized in others. Most 

 strange is the proboscis with the nostrils at the tip, while the incisors which 

 furnish most of the ivory of commerce are almost solely dentine the enamel 

 covering the tip being worn off at an early date (elephants), or forming a 

 band on the outer side (^Mastodon") . 



The DlNOTHERlD^, with the single genus Dinotherium, occur in the 

 miocene and pliocene of Europe and India. In this only the lower incisors 

 are present, and these grow downwards, the symphysis of the jaw being bent 

 so that the teeth form downward-extending tusks. The succession of molar 

 teeth was normal. The animals were about as large as an elephant. 



In the elephants and their near relatives (Elephantid^) the upper 

 incisors form tusks of varying size, the lower are smaller or wanting. The 

 molars bear more than two transverse ridges, and are subject to horizontal 



Fig. 370. Evolution of the teeth of elephants after Flower. A, Mastodon; 

 B, Stegodon ; C, Elefhas (^Loxodon) africanus. Dotted, cement ; obliquely lined, 

 dentine ; heavy black line, enamel. 



replacement. Owing to the shortness of the jaw, and the large size of the 

 molars, not more than two can be in use at the same time. As the more 

 anterior of these becomes worn, it drops out in front, while another takes its 

 place from behind. In some Mastodons transitional types of succession occur. 

 Mastodon (with several sub-generic divisions) extended from the upper mi- 

 ocene through the pliocene, and may have been contemporaneous with man. 

 Its teeth, characterized by from three to six transverse ridges, or ridges broken 

 into tubercles, are common in the northern hemisphere, Africa, and South 

 America. The skeletons are less perfectly preserved. Stegodun. from the 

 later tertiaries of India, etc. Elephas (including Loxodon) embraces the 

 existing elephants as well as the extinct mammoths. In these the valleys 

 between the transverse enamel folds are filled with cement. The living 

 species, E. indiciis and E. africanus occur in India and Africa, respectively. 

 The genus appears in the miocene, the mammoth, E. primigenins of the 

 pleistocene, which became extinct after the appearance of man, being the best 

 known. The discovery in 1799 of frozen mammoth bodies near the Lena 

 delta should be mentioned. The body was covered with close, woolly hair, 

 while a mane on the neck and the hairs on the head were three feet in length. 



