MAMMALS OF MINNESOTA. 59 
ally very wide and curve upward. The orbit is never set off 
from the temporal fossa, by the union of the post frontal pro- 
cesses of the temporal and zygomatic bones. There is in al- 
most every case a deciduate, zonary placenta. The dentition 
is especially characteristic and also difficult to reduce to the 
same general formula. The dentition of the forepart of the 
mouth is, indeed, remarkably uniform throughout the group. 
There are always six incisors in each jaw (except in the single 
case of the sea otter) and two canines. The incisors are usually 
chisel-shaped, and are weil adapted to gnaw the flesh from 
bones of their prey. The canines serve an entirely different 
purpose. They are frequently so long that they lock the jaws 
when they are closed, aud enable the animal to seize its prey 
with a grip which no efforts will suffice to shake off. The size 
and form of the canines constitute, to a certain extent, an in- 
dex of the habits of the animal. The molars and premolars 
constitute a more or less continuous series of variable number. 
The crowns are usually furnished either with sharp cutting 
edges or conical prominences. As the canines indicate the 
habits of the animal especially with reference to the way in 
which they secure their prey, so the molars and premolars 
furnish good evidence of the sort of food constituting the ord- 
inary diet. The lateral extension of both the condyles and 
glenoid surfaces, for the lower jaw prevents that lateral mo- 
tion of the jaws characteristic of herbivorous animals, and in 
harmony with this fact, the molars do not oppose each other, 
but the teeth of the lower jaw fit between those above, and, in 
many cases, their knife-like edges constitute the blades of ver- 
itable shears. There are never more than four premolars in 
one half of the jaw in any living carnivore, and the number 
may be considerably reduced. One of the premolars above and 
below is remarkably developed and furnished with two knife- 
like lobes, and is especially adapted to the cutting of flesh into 
morsels. These sectorials are frequently the iargest teeth and 
are situated so far toward the back of the mouth, that they are 
very effective on accountof the superior leverage their position 
in the jaw occasions. 
The operation of these teeth can be seen when, for instance, 
a cat in biting off a tough bit turns the head to one side and 
closing her eyes, gnashes with a sort of fury, cracking even 
thick bones. Back of these teeth are the true molars which 
have flatter or tuberculated crowns. In the typical carnivores 
these are slightly developed, but they keep pace with the de- 
velopment of omnivorous propensities. 
