252 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



fangs, each of which has its own socket lined with periosteum. Mam- 

 mals have, as a rule, two sets of teeth, the deciduous and permanent 

 teeth ; and when the latter are worn down they usually loosen and fall 

 out, since they undergo little or no repair. An exception to this state- 

 ment is found in the case of the rodents, where the teeth continue to 

 grow from the fact that the fang remains open and the hollow at the 

 base into which the pulp extends the so-called enamel organ is per- 

 sistent, and fresh dentine is constantly being formed within the pulp 

 and fresh enamel upon the anterior surface. The unequal wear of the 

 hard coating of the enamel in front and the dentine behind preserves 

 throughout the whole life of the tooth its chisel-like edge. In many 

 animals sex exercises a remarkable influence on the development of the 

 teeth. Thus, in the anthropoid apes the upper canine teeth in the male 

 are more than twice the size of the analogous teeth in the female ; while 

 the tusks of the bear and of the male elephant and musk-deer are 

 larger than those of the female. So also in the solipedes the canine 

 teeth are absent in the female, while in the ox tribe, although temporary 

 incisors appear aboA r e the gum in both jaws, the permanent incisors are 

 not developed in the upper jaw, but remain in a rudimentary condition 

 within the bone. 



By the formula of dentition, or the dental formula, is meant the con- 

 venient method of reproducing in numerals the number and nature of 

 teeth found in different animals. To distinguish these teeth the letter 

 i is used to indicate the incisors, the letter c the canines, pm the pre- 

 molars, and m the molars. The upper rows of figures represent the teeth 

 of the upper jaw and the lower those of the inferior jaw, the formula 

 usually simply representing the teeth on one side of the mouth; doubling 

 the numbers given therefore represents the total amount of teeth. In 

 the dog the formula is as follows : 



' 



That of the cat is : 



Man: 



1 2-2 ' C l-\ ' Pm 2^2 ' m 3^3 ' 



In herbivora the incisor teeth vary in importance in our grass-feed- 

 ing animals, and are absent in the upper jaw of ruminants, where their 

 place is occupied by the nbro-elastic pad already referred to. . Ruminants 

 have thirty-two teeth, eight incisors and twenty-four molars. In the 

 horse there are two pairs of tushes, or canine teeth, and twelve large 



