VERTEBRATA: MAMMALIA. 



68 1 



only six cervical vertebrae. The teats are two in number and 

 are "thoracic," i.e., are placed on the chest. There are no 

 clavicles, and the digits have no more than three phalanges 



Fig. 378. A, Side-view of young Manatus Americanus ; B, The same viewed 

 from above ; n Nostrils. (After Murie.) 



each. The testes are retained throughout life within the ab- 

 domen, but vesicular seminales are present. The animal is 

 diphyodont (Manatus\ or monophyodont (Halicore) ; the perma- 

 nent teeth consisting of molars with flattened crowns adapted for 

 bruising vegetable food, and incisors which are present in the 

 yotmg animal, at any rate. In the extinct Rhytina it does not 

 appear that there were any incisor teeth; while in all the 

 existing genera, the front of the upper and lower jaws is pro- 

 vided with rough horny pads or plates. 



The only existing Sirenia are the Manatees (Manatus} and 

 the Dugongs (Halicore}, often spoken of collectively as " sea- 

 cows," and forming the family of the Manatidce. 



The Manatees (fig. 380, B) are characterised by the posses- 



sion of numerous 



99 :. n 1 



9-9 



to 



ii ii 



broad molars, which are 



never' all in use at one time, while there are two small upper 

 incisors, which do not cut the gum. The tail-fin is oblong or 

 oval in shape, and the anterior limbs (fig. 379) are furnished with 

 nails to the four outer digits. One species (Manatus Ameri- 

 canus) occurs on the east coast of North America, especially 



