MOLARS. 



197 



The molars in the dog do not form simple arches as in the 

 other animals, but each arch represents a double curve ; so that 

 the two arches on either jaw make the form of a lyre, with its 

 base backward and its apex forward, the widest portion of 



which is on a line between the 

 last premolar and the first 

 molar. The form or curve of 

 the arches varies considerably 

 with the different races of 

 dogs, and increases greatly in 

 those breeds which, by domes- 

 tication, have had their heads 

 and maxillae shortened. These 

 changes may almost approach 

 the nature of a deformity, and 

 the last premolar and first 

 molar may be crowded en- 



FlG. 177. 

 Skull of a greyhound, under surface. 



Fig. 178. 

 Skull of a pug, under surface. 



tirely out of the line of the other teeth, or may be absent, as is 

 sometimes seen in the pug or fancy bull-dogs. 



Dr. James A. Waugh informs me that in the Mexican hair- 

 less dogs the teeth are generally irregular in number and rela- 

 tive position in the jaws. They have no tubercles or trefoils on 



