160 THE VITAL FUNCTIONS. 



growth of the embryo. The rudiments of the 

 human teeth begin to form four or five months 

 before birth : they are contained in the same 

 sockets with the temporary teeth, the capsules 

 of both being connected together. As the jaw 

 enlarges, the second set of teeth gradually ac- 

 quire their full dimensions, and then, by their 

 outward pressure, occasion the absorption of the 

 fangs of the temporary teeth, and, pushing them 

 out, occupy their places.* 



As the jaw bone, during its growth, extends 

 principally backwards, the posterior portion, 

 being later in forming, is comparatively of a 

 larger size than either the fore or the lateral 

 parts ; and it admits, therefore, of teeth of the 

 full size, which consequently are permanent. 

 The molar teeth, which are last formed, are, for 

 want of space, rather smaller than the others, 

 and are called the ivisdom-teeth, because they 

 do not usually make their appearance above 

 the gum till the jierson has attained the age of 

 twenty. In the negro, however, where the jaw 

 is of greater length, these teeth have sufficient 

 room to come into their places, and are, in gene- 

 ral, fully as large as the other molares. 



The teeth of carnivorous animals are, from 



* It is stated by Rousseau that the shedding of the first molar 

 tooth both of the Guinea-pig , and the Capibara, and its re- 

 placement by the permanent tooth, take place a few days before 

 birth. Anatomic Comparee du systems dentaire, p. 164. 



