Prof. Owen on the Class Mammalia. 13 
Carnivora, e. g. the front-teeth have broad tuberculate summits, 
adapted for nipping and bruising, while the principal back-teeth 
are shaped for cutting, and work upon each other like the blades 
of scissors. The front-teeth in the Elephant project from the 
upper jaw, in the form, size and direction of long pointed horns. 
In short, shape and size are the least constant of dental charac- 
ters in the Mammalia; and the homologous teeth are determined, 
like other parts, by their relative position, by their connexions, 
aud by their development. 
‘hose teeth which are implanted in the premaxillary bones, 
and in the corresponding part of the lower jaw, are called ‘inci- 
sors,’ whatever be their shape or size. The tooth in the maxillary 
bone which is situated at or near to the suture with the premax- 
illary is the ‘canine,’ as is also that tooth in the lower jaw, 
which, in opposing it, passes in front of the upper one’s crown 
when the mouth is closed. The other teeth of the first set are 
the ‘deciduous molars;’ the teeth which displace and succeed 
them vertically are the ‘premolars;’ the more posterior teeth, 
which are not displaced by vertical successors, are the ‘ molars’ 
Three of the seven teeth may be ‘premolars,’ and four may 
be true ‘ molars ;’ or there may be four premolars, and three true 
molars. This difference as | have own, forms a 
character of a secondary group or order in the mammalian class,* 
The essential nature of the distinction is as follows: true molars 
The Gymnure, the Mole, and the Hog are among the few ex- 
isting quadrupeds which retain the typical number and kinds of 
a MF se of a Classification of the Mammalia, Trans. Zool. Soe. yol. ii, p. 330 
