NO. 2 EXTINCT HORSE FROM ALASKA — HAY \J 



were extraordinarily short, 30 mm. ; while in other horses examined 

 by him the length ranged from 41 mm. to 53 mm. In the Alaska 

 skull these slit-like openings are 29 mm. long. In a number of skulls 

 of Grant's zebra these fissures vary greatly in length. 



It remains to compare the teeth of the Liakhof skull with those 

 of the Alaskan. They differ little in measurements. The length of 

 the premolar-molar series in the former, measured in a straight line, 

 is 170 mm., exactly that of the Alaskan skull. In the following table 

 the measurements of both are given for easier comparison. 



Measurements of Teeth 



Liakhof horse Alaskan horse 

 Teeth mm. mm. 



Pm. 2 , length 41 39 



width 24 26.5 



protocone 10 9.5 



Pm. s , length 2.7 30 



width 29 28 



protocone 13 12 



Pm. 4 , length 26 28.5 



width 3°-5 28.5 



protocone 14 15 



M.\ length 24 25.5 



width 28.5 27.5 



protocone 13.5 12 



M. 3 , length 23.5 26 



width 27.5 26 



protocone 15 12 



M.*, length 29 26.5 



width 25 24.5 



protocone 16 13 



It will be seen that there are no remarkable differences in the 

 dimensions of the teeth, probably not greater than would be found 

 in different individuals of the same species. The Liakhof skull, hav- 

 ing belonged to an older horse, would naturally be expected to have 

 the anterior premolar and the hinder molar longer, and the others 

 shorter, on the grinding surface, than the younger horse. The proto- 

 cones are of about the same length, except that those of the hinder 

 molars of the Liakhof skulls are 3 mm. longer than those of the 

 Alaskan skull. 



As far as can be judged from Tscherski's figure the arrangement 

 of the enamel around the two cement lakes of each tooth appears to 

 be not especially different from that seen in the Alaskan skull. A 

 considerable difference is seen, however, in the valleys which enter 

 the interior of the tooth on the inner side. The median, or postproto- 



