. An introduction to the study of mammals living and extinct. Mammals. 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 prem
. An introduction to the study of mammals living and extinct. Mammals. 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 jolates, 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 a
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