Eassie — Some Variations in the Skeleton of the Domestic Horse. 327 



found in the relative length of the arm. In the fossil ancestors of the horse, 

 from the five-fingered and five-toed animal of the lowest Eocene formations, 

 through the whole series to the horse of recent formations, the humerus has 

 gradually been shortened in relation to the bones below it. In the various 

 races of horses of the present day, there is a variability in the lengtli of the 

 humerus, apparently due to the fact that some are more advanced than 

 others as regards this evolutionary shortening. It seems to me tliat the 

 ultimate shortening determines perfection of function of the limb of the horse. 



In the work by Goubaux and Barrier on " Tlie Exterior 

 of the Horse,"' it is sliown that a large scapula for the attach- 

 ment of the muscles, and a sliort humerus, are of advantage 

 as regards speed. I have attempted to show this in the 

 diagram, fig. 7. It will be evident that the long humerus 

 gets as far as {a) while the sliort humerus reaches (6), a 

 point far in advance of («), describing only the same length 

 of arc. It is beyond question therefore that a sliort humerus 

 is requisite for speed. 



But a short humerus determines something even more 

 important. To begin with, I find no appreciable variation "lo- '• 



in the angle of the scapula with the humerus. It is always a little more 



than a right angle (fig. 8). There is, however, admittedly, a wide difference 

 in the angle at the elbow. When the humerus is long, it is recumbent ; 



' 'I'ranslated from the Second l<'reiich Ediliou by S. J. J. Harger, i'hiladelpljia, 1892, 



