188 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Measurements of skulls. 



On comparing the atlas of No. 7706 with, that of a specimen of 

 B. hison certain differences are found, but it will requhe further 

 comparisons in order to determme whether these differences are con- 

 stant. When in the two atlases the distance from the outer end of 

 the anterior articular surface to the outer end of the hinder articular 

 surface is taken, it is found that in B. hison this is 48 per cent of the 

 greatest width of the bone, while m B. alleni it is only 43 per cent. 

 The notch in front of the neural arcli is deeper than in the case of 

 B. hison. The notch m front of the centrum is relatively and abso- 

 lutely narrower in the fossil than ux the living species. The mner 

 borders of the foramina seen on the lower surface of the atlas have 

 exactly the same distance between them in the atlas (greatest width 

 210 mm.) of the living bison as m the much wider atlas of B. alleni. 

 In the latter, therefore, these foramma are much farther removed 

 from the outer borders of the bone. In the American bison there is a 

 much broader bar of bone runnmg from the outer hmder angle of the 

 wing to the hypophysis than m B. alleni. The atlas figured by 

 Allen ^ seems in the latter respect to resemble more closely B. hison. 



The axis. — This bone is completely preserved. The following are 



some of the dimensions. In the second colunm are the correspondmg 



measurements from a mounted bison in the United States National 



Museum. 



Measurements of axis. 



1 The American bisons, pi. 2, 



