92 



GENERAL ZOOLOGY 



Mammals belonging to the order Carnivora have strong, 

 recurved canine teeth, poorly developed incisors, and high 

 crowned premolars and molars. In such animals the jaws have 

 practically no side play, a condition which reaches its highest 

 development in cats, in which the cheek teeth have a purely 

 shearing action on food. In dogs, the premolars are shearing 

 teeth, but the molars are adapted for grinding or crushing (Fig. 

 56). Omnivorous bears, such as the common black bear, lack 

 shearing teeth but do have well-developed grinders. Carrion- 



Fig. 59. — Side and ventral view of the upper teeth of the ox. 



molars. 



p, premolars; M, 



eating forms have blunter teeth, while fish eaters such as the seal 

 have teeth that are all pointed and prehensile in function (Fig. 57). 

 Some of the plant-eating animals belonging to the Ungulata, 

 hoofed animals, illustrate a high degree of specialization which 

 contrasts strongly with the conditions found in the teeth of 

 typical Carnivora. Incisors may be present in both jaws and 

 adapted for seizing or cutting as in the horse; but in ruminants, 

 such as the ox, they are absent in the upper jaw, which, instead 

 of teeth, is provided with a tough pad against which the incisors 

 of the lower jaw bite (Fig. 59). The tusks of the elephant 

 are highly modified incisors. Canine teeth as a rule are not well 



