SIEENIA AND CETACEA. 



309 



hony rays. The hind-limbs are vjholly ivanting} and there is 

 no sacrum. The anterior liinhs are converted into sioimming- 

 paddles or " fli23pers!' The s?iout is fieshy and ivell-dxr eloped, 

 and the nostrils are placed on its upper surface, and not on 

 the top of the head, as in the JVliales. Fleshy lips are present, 

 and the upper one usually carries a moustache. The skin is 

 covered with sccdtered bristles. The head is not dispropor- 

 tionately large, as in the true Whales, and is not so gradually 

 prolonged into the body as it is in the latter. There may 

 be only six cervical vertebras. There are no clavicles, and 

 the digits have no more than three phalanges each. The 

 animal is diphyodont (Manattcs) or monophyodont [Halicore] ; 

 the permanent teeth consisting of molars loith flattened croions 

 adapted for bruising vegetable food, and incisors ivhich are 

 present in the young animal, at any rate. In the extinct 

 Rhytina it does not appear that there were any incisor teeth. 

 The only existing SircnicL are the Manatees {Manatus) and 



Pig. 617. — A, Side-view of tlie skull of the Dugong {Halicore), showing the tusk-like upper 

 iucisors ; b, Side-view of the skuU of Manatee {Manatus). (After Cu%'ier.) 



the Dugongs {Halicore), often spoken of collectively as " sea- 

 cows," and forming the family of the Mancdidce. 



The Manatees (fig. 617) are characterised by the posses- 

 sion of numerous molar teeth, and of tw^o small upper in- 

 cisors, which are wanting in the adult animal. They are 

 large animals, ten feet or more in length when fully grown, 

 and they live in shallow water near the coast, or ascend 

 rivers for considerable distances, their food being principally 

 aquatic plants. 



^ All the Sirenia possess a rudimentary pelvis, and in the extinct Halitherium 

 a small femur is present in addition. 



