TEETH OF DIOPHYODONTS. 301 



Rabbit, retain their usual relations with the premaxillaries, thus 

 proving, a fortiori, that the tooth which projects anterior to them 

 must also be an incisor. 



The law of the unlimited growth of the scalpriforai incisors is 

 unconditional ; and constant exercise and abrasion are required 

 to maintain the normal and serviceable form and proportions of 

 these teeth. When, by accident, an opposing incisor is lost, or 

 when, by the distorted union of a broken jaw, the lower incisors 

 no longer meet the upper ones, as sometimes happens to a wounded 

 hare, the incisors continue to grow until they project like the 

 tusks of the elephant, and their extremities, in the poor animal's 

 painful attempts to acquire food, also become pointed like tusks. 

 Following the curve prescribed to their growth by the form of 

 their socket, their points often return against some part of the 

 head, are pressed through the skin, 

 then cause absorption of the jaw-bone, 

 and again enter the mouth, rendering 

 mastication impracticable and causing 

 death by starvation. I have seen a 

 lower jaw of a beaver, in which the 

 scalpriform incisor has, by unchecked 

 growth, described a complete circle. 

 The point had pierced the masseter Forepart of upper jaw of a nai.iMt, \\-mi 



, i - ,1 T i n ,1 incisors of abnormal growth. 



muscle, and entered the oack ot the 



mouth, passing between the condyloid and coronoid processes of 

 the lower jaw, descending to the back part of the molar teeth, 

 in the advance of the part of its own alveolus, which contains its 

 hollow root. The upper jaw of a Rabbit, with an analogous ab- 

 normal growth of the scalpriform and accessory incisors, is shown 

 in fig. 239. 



D. Insectivora.- -The dental system in this order is remarkable 

 for the many varieties and even anomalies which it presents- 

 almost the only characteristic predicable of it being the presence 

 of sharp points or cusps upon the crowns of the molar teeth, 

 which are always broader in the upper than in the lower jaw. 

 The teeth that intervene between these and the incisors are most 

 variable in form and size, but are never absent ; the incisors 

 differ in number, size, and shape, in different species, the anterior 

 ones approximating in some species to the character of the scalpri- 

 form teeth of the Rodents. They may be wholly absent in the 

 upper jaw, fig. 242, A. 



The Chrysochlore, or iridescent Mole of the Cape, makes the 

 nearest approach, by the number of its molar teeth, fig. 240, to 



