MAMMALIA. 393 



There are eight on each side of the upper, and also of the 

 lower jaw; thus amounting in all to thirty-two.* 



A few species of mammalia, as the Ant-eaters, are entirely 

 devoid of teeth; in others there is a great diversity as to their 

 number. The female Narwhal has two teeth, and both are 

 concealed in the substance of the jaw. The Australian Water- 

 rats have twelve. Most gnawing animals have twenty; but 

 the Hares and Rabbits have twenty-eight. The Porpoise has 

 between eighty and ninety, and the true Dolphins from one 

 hundred to one hundred and ninety, f 



It is found that the arrangement of the teeth varies, 

 according as the food is to consist of animal or vegetable 

 substances, of soft flesh or horny covered insects: of tender 

 herbs, or wood of greater or less degrees of hardness. Hence 

 it is possible, merely by an inspection of the teeth, to deter- 

 mine, with considerable certainty, the diet, the habits, and 

 even the general structure of most of the mammalia. J 



We never meet in nature with an incongruous union of 

 parts. A Lion, with the hoof of a Horse, could not subsist; 



Fig. 297. SKULL OF A GNAWING ANIMAL. Fig. 298. SKULL OF A BOAR. 



it would die of hunger from inability to seize and retain its 

 prey. In like manner, a Horse, with the teeth of a Lion, 

 would starve in the midst of the finest pastures, from being 

 unable to crop and triturate its food. 



* Zoologists have adopted a formula for expressing the number of teeth 

 possessed by different animals at each side of the month, distinguishing 

 those in the upper jaw from those in the lower jaw. The dental formula 

 of man is written thus : 



2 2 11 2 2 3 3 



Incisors ; Canines ; Premolars -; Molars ; = 32. 



2 2 1 1 22 3 3 



f Owen's Odontography. 

 j M. Edwards' Elemens. 



