MAN ATI D^; 217 



backwards considerably behind the orbits. Their sides are formed 

 by the ascending processes of the premaxillse below, and by the 

 supraorbital processes of the frontals above, no traces of nasals 

 being found in most skulls, though these bones are occasionally 

 present in a most rudimentary condition, attached to the edges 

 of the frontals, far away from the middle line, in a position 

 quite unique among the Mammalia. In front of the narial aper- 

 ture the face is prolonged into a narrow rostrum, formed by 

 the premaxillse, supported below and at the sides by the maxillae. 

 The under surface of this is very rugose, and in life covered by a 

 horny plate. The rami of the mandible are firmly united together 

 at the symphysis, which is compressed laterally, slightly deflected, 

 and has a rugose upper surface ; to this another horny plate is 

 attached, which, with that of the upper jaw, functionally supplies the 



FIG. 72. Skull of African Manatee (Manatus senegalensis). \ natural size. 

 From Mus. Roy. Coll. Surgeons. 



place of teeth in the anterior part of the mouth. In the young 

 state there are rudimentary teeth concealed beneath these horny 

 plates, which never penetrate through them, and must therefore be 

 quite functionless, and altogether disappear before the animal is full- 

 grown. There is besides on each side of the hinder part of both 

 upper and lower jaws, a parallel row of molar teeth, similar in 

 characters from the beginning to the end of the series, with square 

 enamelled crowns raised into tuberculated transverse ridges, some- 

 thing like those of the Tapir and Kangaroo. The upper teeth have 

 two ridges and three roots; the lower teeth have an additional 

 posterior small ridge or talon, and but two roots. These teeth 

 succeed each other from before backwards, as in the Proboscidea, 

 those at the front of the mouth being worn out and shed before 

 those at the back are fully developed. There are altogether about 

 eleven on either side of each jaw, but rarely more than six are 



