310 DECIDUOUS AND PERMANENT TEETH OF HOG. 



The hog is one of the few existing quadrupeds which 

 retain the typical number and kinds of teeth. 



Figure 75, part of the lower jaw of a young hog, illus- 

 trates the phenomena of development which distinguishes 

 the premolars from the molars. The first premolar, /> 1, 



DECIDUOUS AND PERMANENT TEETH OF THE HOG. 



and the first molar, m 1, are in place and use, together 

 with the three deciduous molars, d 2, d 3, and d 4 ; the 

 second molar, m 2, has just begun to cut the gum ; p 2, 

 p 3, and p 4, together with m 3, are more or less incom- 

 plete, and concealed in their closed alveoli. 



The premolars must displace deciduous molars in order 

 to rise into place; the molars have no such relations. It 

 will be observed that the last deciduous molar, d 4, has 

 the same relative superiority of size to d 3, and d 2, which 

 m 3 bears to m 2 and m 1 ; and the crowns of p) 3 and p> 

 4 are of a more simple form than those of the milk-teeth 

 which they are destined to succeed. 



The germ of the permanent canine has not yet appeared 

 below the deciduous one, c ; those of the permanent in- 

 cisors, i 1, i 2, i 3, are seen ready to push out the decidu- 

 ous incisors d\^d 2, d 3. When the whole of the second 



