No. 499] INCISORS OF MARMOT A MOXAX L. 459 



the anterior portion of the tooth, and the more rapid 

 wearing of the posterior edge keeps these front teeth 

 chisel-like and sharp. 



The abnormal growth of the incisors will occur when- 

 ever the upper and lower teeth fail to meet. An injury 

 to either jaw, as for instance a bullet wound, might de- 

 stroy the perfect opposition of the incisors. But the 

 teeth in this specimen are sharp pointed and not worn 

 at the distal end, as they would be if they had ever func- 

 tioned properly, which fact would indicate that the wound 

 must have occurred before the permanent teeth appeared. 



A careful examination shows that the abnormality can 

 be accounted for in another way. The socket of the left 

 incisor is not normal in its position, and the tooth itself 

 grows inward toward the right incisor, striking it about 

 8 mm. from the jaw. The latter tooth has on its inner 

 side a groove extending from near the distal end to the 

 point where the two incisors are in contact. This groove 

 was produced by the pressure of the left incisor upon 

 the right, and this pressure is undoubtedly the cause of 

 the failure of both teeth to meet the lower ones. The 

 abnormal growth then depended primarily upon a con- 

 genital abnormality in the position and direction of the 

 socket of the left incisor. One of the lower teeth of the 

 same skull was found, but has been misplaced. Mr. Goff 

 informs me that it also was curved and much longer than 

 usual. 



It would be of interest to know how the animal with 

 this curious set of teeth obtained food sufficient to prevent 

 starvation. It may well be that this abnormality was 

 the chief determining factor in its struggle for existence. 



