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SCIENCE. 



ON THE OVERGROWN TEETH OF FIBER 

 WIBETHICUS. 

 By Herman L. Fairchild. 



No group of animals is more clearly marked by a 

 single feature than the Rodentia by their peculiar incisor 

 teeth. Except in the Rabbits which have a supplemen- 

 tary pair in the upper jaw, the number is always four. 

 The enamel is mostly, sometimes wholly, on the anterior 

 surface ; where also the dentine is harder. The constant 

 abrasion consequently preserves a keen chisel edge which 

 admirably adapts them for gnawing. This purpose re- 

 quires them to be of a certain length. To keep that 

 length, the loss from wear is compensated by continual 

 outward growth frcm the base, the growth being sup- 

 plied from permanent pulp. The outward growth and 

 the terminal wear are nicely balanced. 



It is evident that a loss of one incisor prevents ab- 

 rasion of the opposing tooth, which, continuing to push 

 outward, may become so long as to interfere with the 

 proper use of the jaws and the remaining teeth. Such 

 cases, while not unknown, are sufficiently rare to be of 

 great interest to the naturalist, and] of wonderment to 

 the unscientific. 



* Fig. I, represents a striking example of such malforma- 



FIC 1 



tion in the case of a muskrat, Fiber Wibethicus. The 

 figure is three-fourths the size of the specimen. This skull 

 was found on the bank of Sacandaga River, town of 

 Edinburgh, Saratoga Co., N. Y. Unfortunately no other 

 portion of the skeleton was collected ; but the most un- 

 observing could not fail to notice such remarkable teeth. 

 It was naturally supposed that some strange creature 

 had been discovered. Falling into the hands of the 

 writer its character was discovered and a normal speci- 

 men was procured for accurate comparison. The latter 

 is shown in figure 2. 



When removed from their sockets the overgrown in- 

 cisors show a growth nearly to a complet circle, although 

 the curvature is somewhat spiral. Their terminations 



•This illustration was used, without comment, in an article by the 

 writer in the 1'opulur Science Monthly for June, 1880. 



exhibit the normal form produced by abrasion at a time 

 when the teeth were of the proper length, and are natur- 

 ally discolored with foreign matter on account of long 

 disuse. The yellow color of the front surface of these 

 incisors is fainter towards the ends, but still marked. 



As the mandible is missing it is impossible to know 

 what was the difficulty with the lower incisors. They 

 might have been broken by severe usage or carried 

 away by a gun-shot. But that the animal once possessed 

 them is shown by the naturally abraded ends of the re- 

 maining ones. The trouble seems to have been of a 

 character which prevented the after growth of the lower 

 incisors. For if they had grown out again after an in- 

 jury, they would have been forced to take a position in 

 front of the lengthened upper incisors. This would have 

 prevented the forward and backward motion necessary 

 for mastication, and so prominent in Rodents, and more- 

 over would undoubtedly have worn the anterior surfaces 

 of the overgrown upper teeth. But the latter do not 

 show the least unnatural abrasion, while the molars do 

 show that they were used. Probably the breaking of the 

 teeth near the bone would have so exposed the pulp as 

 to destroy it and the implanted part of the injured teeth. 



The fairly clean fresh surfaces of all the upper molars 

 would indicate that the lower molars were quite intact 

 and that the greatly lengthened teeth did not interfere 

 with mastication, however much they interfered with pre- 

 hension. The accumulation of foreign matter upon the 

 sides of the molars is greater than on those of the normal 

 skull. Perhaps this is due to less discrimination in choice 

 of food, and possibly to somewhat greater age. 



That the animal lived some considerable time after its 

 misfortune, is proven by the great length of the teeth. The 

 time required for this growth is unknown. It is, however, 

 a very interesting point and should be determined. The 

 rate of growth of the incisors may vary, possibly in the 

 same individual, according to the kind of food and conse- 

 quent wear; at least it would not be right to assume that 

 the rate of growth is always the same. Observation up- 

 on a Rabbit or other rodent would be valuable but not 

 conclusive, as the rabbit is entirely vegetarian in diet while 

 the Muskrat is quite omnivorous. To answer the ques- 

 tion before us, the observation should be made upon a 

 Muskrat having the lower incisors removed or rendered 

 useless, in order to repeat as nearly as possible the con- 

 ditions under which we imagine our specimen existed. 



As the ends of the overgrown incisors had long passed 

 the point of greatest interference they did not prevent the 

 taking of food with the mouth ; and the creature prob- 

 ably did not die from starvation. 



If the readers of " Science " can give any facts bear- 

 ing on this matter from their personal knowledge and ob- 

 servation they will confer a favor by sending them to these 

 columns. 



In Forest and Stream of April 4, 1878, there is a sketch 

 of a Woodchuck's skull showing an abnormal lengthening 

 of both pairs of incisors, which, according to the descrip- 

 tion, did not prevent the animal from procuring sufficient 

 food to keep it in good condition. And Owen's " Odonto- 

 graphy" briefly describes (page 41 1, old ed.) the abnor- 

 mal elongation of the incisors of rodents ; and notices the 

 skull of a beaver, of which a lower incisor formed a com- 

 plete circle. Plate 104, Fig. 7, of the above work, also 

 shows the abnormal upper incisors of a rabbit. 



Absorbing Power of the Atmosphere. — M. Laight had 

 long ago shown that the radiating light of the sun is largely 

 absorbed by the layer of atmosphere. But penetrating more 

 deeply into the question, he has successively and separately 

 studied the absorption undergone by each ray of the spec- 

 trum. He concludes thai these diverse rays are from being 

 equally absorbed, and that the radiation is modified accord- 

 ing to the degree of absorption. One ol the results of this 

 interesting fact is that the color of the sun is different from 

 that which we attribute to him. 



