254 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the molar arches of the upper jaw are wider apart than those of the lower 

 jaw : and when the molars are in contact the incisors do not touch, thus 

 saving unnecessary wearing. 



In the omnivora, as represented by the hog, there are forty-four 

 teeth, — twelve incisors, four canine or eye teeth, twenty-four grinders, and 

 four so-called wolf-teeth. 



In the carnivora three kinds of teeth are met with. They are the 

 incisors, which are twelve in number, are sharp and cutting, and when 

 first erupted have three cusps on their free extremity, the lateral cusps 

 being on a lower plane than the central cusp. They thus, therefore, 

 resemble a fleur-de-lis. In carnivorous animals the two central incisors 

 are smaller than the next two, and these smaller than the next teeth. The 

 canine teeth are four in number, two in each jaw, and attain considerable 

 length, being larger in the upper jaw than in the lower, are pointed and 

 curved backward. The molars are variable in number, augmented in 

 volume from the first to the penultimate, which has large cusps and is 

 termed the dens sectorius. The teeth of carnivorous animals, with the 

 exception of the incisors, preserve their pointed form unaltered. 



In the dog the first three molars of the upper jaw do not come in 

 contact with the first four molars of the lower jaw, which correspond to 

 them, even when the mouth is closed. The highest cusp of the dens 

 sectorius, however, rests on the posterior surface of the first tuberculated 

 molar of the upper jaw. The incisors are cutting teeth, the canines tear- 

 ing, and the molars crushing or cutting, like scissors, but not grinding 

 in function. 



The character and shape of the teeth vary in the different members 

 of the carnivorous group ; in the bear, which is essentially in type car- 

 nivorous, but which is an omnivorous animal, the molars are less pointed 

 than those of the pure carnivora, and approach in nature the shape 

 * of the teeth of omnivora, of which man may be taken as a type. In 

 the cat tribe all the teeth are very pointed. 



The teeth are mechanical instruments without sensation, but serve 

 as conducting organs of sensibility, like the hair ; since in man they are 

 sensitive to cold, therefore they are also probably sensitive in other 

 animals. They transmit sensations of resistance, which must be less 

 acute in animals, such as the . carnivora, which are accustomed to 

 crush bones, and thus convey information as to the solidity of matters 

 between the teeth and regulate the degree of muscular effort required in 

 mastication. The articulation of the teeth with the alveoli is in the form 

 of a pyramid whose base is external. In mastication, therefore, pressure 

 is transmitted to the bony walls of the alveoli, and the sensitive pulp is 

 protected, unless the teeth are loose in their sockets, when mastication 

 becomes. painful. 



