MASTICATION. 31 



[The law based on a harmony of organization between the 

 teeth and their uses and between the teeth and other organs of 

 the body must be used with great caution. A universal law of 

 organic harmonies no doubt exists, but its true nature has not 

 yet been discovered. Cuvier, who boasted so much of this law, 

 nevertheless used it with the utmost caution, and never trusted 

 wholly to it. K. KJ 



Fig. 27. Skull of the young Narwhal, before the development of the 

 left incisive, which sailors call its horn* 



Of all the teeth the molars are the most useful : hence their 

 presence is much more frequent than the incisives or ca- 

 nines. These latter, for an obvious reason, are never wanting 

 in the carnivora; but they are not unfrequently absent in the 

 herbivora. 



[The reason is not at all obvious, even where it is the case ; 

 such teeth are wanting in the strictly carnivorous cetacea. 

 K. K.] 



The canine in some animals grow to a large size, and 

 become instruments of attack and defence (Fig. 28). 



54. At birth it is seldom that the human teeth have cut 

 the gums ; they appear usually from six months to a year 

 after birth. The teeth which first appear are called milk 

 teeth, or deciduous, as destined to be thrown off and to be 

 replaced by others. They are twenty in number, namely, in 

 each jaw ten viz., four incisives, one canine, and two molar. 



