MAMMALIA. 433 



Those grinders which replace milk teeth are sometimes called 

 premolars. The true molars do not have any representatives 

 in the milk set. The corresponding teeth in the lower jaw are 

 similarly named. The typical number of teeth is forty-four, 

 eleven in each half-jaw. This may be shown by a formula in 

 which the numerator indicates the number of each kind in one 

 half of the upper jaw and the denominator a similar portion 

 of the lower : i. f , c. y , p. | , m. f 44. This means that there 

 are three incisors, one canine, four premolars, and three molars 

 in each half jaw, both above and below. The dental formula 

 for adult man is : i. |, c. { . p. \ , m. f = 32. The numbers are 

 not always the same in the upper and lower jaw. 



445. Supplementary Studies. Let the student determine by examina- 

 tion, and write the dental formula of the cat, dog, horse, cow ; milk set 

 in man. 



Compare the molars of some carnivorous animals with those of some 

 herbivorous; similarly the canines. Describe the action of the jaws in the 

 act of chewing in the dog, cow, rabbit, horse. 



446. The Digestive Organs present the same regions and 

 general arrangement found in the typical vertebrates. There 

 are usually fleshy and movable lips covering the teeth. Some- 



P 



FIG. 231. Diagram of stomach of dog (A) and rat (B). After Wiedersheim. 



times these are much extended and in connection with the nose 

 may become important organs (snout, proboscis) for the cap- 

 ture of food. The stomach varies widely but is ordinarily a 



29 



