122 Bulletin American Museum of Natural History [Vol. LXXII 



that was not clearly the direct result of some individual pathological 

 condition. However, one skull of Dendrohyrax. d. nigricans in the col- 

 lections of the American Museum is exceptional in a distinct warping of 

 the skull. Here the right side is longer than the left, the difference 

 being most obvious in the occipital region. Correlated with this asym- 

 metry is a difference in the upper tooth rows, that of the right side being 

 nearly straight, that of the left clearly bowed. 



Dental Anomalies in the Hyraxes 



Parallel to the cases so frequently encountered among the rodents, 

 where too the proper occlusion of the persistently growing incisors is 

 dependent on even wear of the tips, are hyraxes in which the upper 

 incisors, unopposed by wear below, grow in great arcs. No specimen in 

 the Congo collection shows this anomaly, but the American Museum 

 possesses one skull of this type picked up b}^ Dr. Chapin on Mt. Kenya 

 at an altitude of 14,000 feet. The specimen is that of a Procavia j. 

 mackinderi. 



Another similar anomaly occurs in a specimen of an old male Dendro- 

 hyrax d. emini in which one of the upper incisors had been lost long be- 

 fore death and the two lower incisors, which would normally oppose this 

 tooth had grown forward about twice as far as the corresponding teeth 

 on the opposite side. This same individual had suffered a broken zygo- 

 matic arch on the same side as the tooth loss, at what was probably the 

 same time. Most of the chewing teeth had been broken and destroyed 

 during life and it appears that this ancient hyrax may have died through 

 the accidents to which his dental equipment had been subjected. 



The first permanent teeth to wear completely away are the first 

 molar above, the first molar below. These teeth are fully func- 

 tional and well worn before the deciduous fourth premolar is shed and 

 before the second molar is up in position. The condition in which the 

 first molar is worn down to the roots is encountered in all of the genera 

 of hyraxes, and is not uncommon, but specimens in which the second 

 molar is also worn out are rare. I have encountered no skull in which 

 the crown of the third molar has disappeared. 



Sexual Characters in the Skulls 



The sexual dimorphism of the upper incisors was established by 

 Thomas (1892, P. Z. S., p. 54). As he pointed out, in some species the 

 dimorphism is not well marked. It is, however, firmly established in 



