84 Surgical Diseases and Surgery of the Dog 



two external and one internal, each supporting a tubercle. The first 

 true molar of the lower jaw is the sectorial of that series and is the 

 largest tooth in the entire mouth. It possesses two firmly implanted 

 roots. This tooth opposes the fourth premolar of the upper jaw in a 

 scissor-like manner. When the dog wishes to divide tough meat or 

 bones he passes them back to these teeth and makes a shearing 

 movement by several short quick strokes of the jaw. The remain- 

 ing two true molars are quite small. The second is two-rooted but 

 the last possesses only one root. 



The period at which both deciduous and permanent teeth are 

 erupted varies in different races and the sexes. In the larger breeds 

 and in females they appear somewhat earlier than amongst the 

 smaller animals and males. At birth the gums are smooth. Towards 

 the end of the third week the deciduous canines make their appear- 

 ance, about the twenty-fifth day the comer incisors, about the 

 twenty-eighth day the middle incisors, and about the thirtieth day 

 the pincers. The superior temporary incisors are cut before the 

 inferior. 



At two months the permanent inferior pincers are seen to 

 pierce the gum, and by the fifth month all the permanent incisors 

 are up and in wear. The permanent canines are cut between the fifth 

 and sixth months. At the end of the sixth or seventh week the 

 second, third, and fourth premolars are in place, and between 

 the fourth and sixth months they give way to their permanent 

 successors. The first molar is erupted at about the sixth month and 

 the second during the seventh month. The first premolar appears 

 between the fourth and fifth months. Between the sixth and 

 eighth months the dog has acquired a full set of permanent teeth. 



During the first few years of life the age may be approximately 

 gauged by the appearance of the four inner incisors of both jaws, 

 the lateral cusps of which gradually disappear. These changes can- 

 not, however, be absolutely relied upon since the extent to which 

 they take place depends more or less on the wear occasioned by the 

 animal's food, and the health of the organs themselves. After the 

 first year the middle cusps begin to wear even with the lateral from 

 the two central incisors of the lower jaw. The same change takes 

 place in the two adjoining teeth in the following year. After the 

 third year the cusps are lost in the two central incisors of the upper 

 jaw, and their two neighbors undergo the same change after the 

 fourth year. 



