CHAPTER IX. 



ANATOMICAL PECULIARITIES OF THE TEETH IN 

 RELATION TO INJURY AND DISEASE. 



MANY troubles and disasters arise in animals in conse- 

 quence of injuries to their teeth, and injuries, trivial in 

 one mammal, may in another be fraught with serious 

 results, due to variations in the use and specialization of 

 the dental organs. 



We may commence this subject with the kangaroo. 

 This mammal has three incisors in the upper jaw, but 

 only one in the mandible. This lower incisor is procum- 

 bent and flattened from side to side; the outer surface 

 is slightly convex, the inner flat, but has a median ridge ; 

 the margins of the tooth are sharp. The lower incisor, 

 instead of an-tagonizing the upper teeth by means of its 

 tip, or crown, meets them along its sharp outer margin 

 (fig. 107). The lower incisor is provided with a large 

 persistent pulp ; the pulp chamber, contrary to what is 

 usual in teeth, extends nearly to the tip. The points of 

 these teeth, shaped something like a lancet, are exceed- 

 ingly thin and brittle. As a consequence, the tips are 

 easily broken, and if only a small piece is detached, the 

 pulp is exposed (fig. 108). Kangaroos, like mammals of 

 even high moral pretensions, have domestic differences, 

 which occasionally lead to unpleasant consequences. In 



