5] 2 Vertehrata. 



domesticated : the African Elephant {E. africanvs), with fewer, 



thicker plates ; and very large ears. 



The extinct forms are numerous. The M a m m o t h (^. primigenius), from 

 the Quartemaries of Siberia and Europe, ap- 

 proached the Indian Elephant in build, but 

 had a thick coat of hair to fit it for the raw 

 climate. The Mastodons were aberrant forms, 

 with several molars in use at once ; the molar 

 ridges are few, and not connected by cement. 

 Some forms had a larf;e incisor in the mandibu lar 

 ramus turned foi-wards and downwards; they 

 also had upper incisors like those of the Elephant. 

 The two genera, Mastodon and Elephas, are closely 

 connected by their outlying forms: Tertiary. The 

 Miocene genus, Binotheriv/m, had relatively small 

 molars, like those of the Tapir ; the upper incisors 

 were absent, but iin each jaw there is a single 

 downwardly- directed incisor. 



theriL, *^''' ^^^ °* ^^™' '^^'^ Senus Binoeeras, recalls the Elephants in 



size and form, and is associated with them : it 

 difEers, however, in many respects ; there are no 



incisors in the premaxilla (six in the lower jaw), but there are very large upper 



canines ; the molars are small : Miocene of North America. 



Order 7. Sirenia {Sea Cows). 



The Sirenia, a small group of marine Mammalia, were formerly 

 classed with the Whales ; they have, however, absolutely no connection 

 with them. The resemblance in certain structural points, is to be 

 regarded as dependent upon adaptations to a similar mode of life. 

 In some respects this group recalls the Ungulata. 



The body has a sparse covering of bristles. The head is borne upon 

 a very short neck, but is well marked off from the trunk ; the nares 

 lie at the end of the snout ; the lips are large and thick ; pinnse are 

 absent. The trunk passes gradually into a powerful tail, at the end of 

 which there is a large horizontal fold of skin on each side, the two 

 folds together forming the " caudal iin." The fore limbs are short 

 and fin-like, with the digits enclosed in a common membrane; the 

 thumbs are rudimentary ; the others, three-jointed (in contradistinc- 

 tion to the Whales) ; the arm is not movable at the shoulder only, 

 as in Whales, but also at the elbow ; in the Manatee, rudimentary 

 hoof-like nails occur. Hind limbs are altogether wanting in all 

 living Sirenia, and the pelvis is vestigial; but in the Miocene genus, 

 Mdlitherium, traces of the hind limbs in the form of rudimentary 

 femurs have been found ; the two mammae lie between the fore limbs. 

 In young forms, upper and lower incisors are present, but they 

 usually fall out, so that the adult is edentulous anteriorly; in the 

 piale Dugong alone, a pair of upper incisors develops into tusks ; in 



