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 well 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 largest teeth and 

 are situated so far toward the back of the mouth, that they are 

 very effective on account of 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. 



