22 Williams, Fisher, and Udall: The Spavin Group. 
quency and extent of these injuries. Were the question pro- 
pounded, in what two animals are strains most common; doubt- 
less the uniform answer would be, man and horse, some placing 
the one, some the other, first. Carefully examined comparatively, 
they represent the extremes in anatomical structure and attitude 
among the higher mammalia. 
Comparing the thoracic limbs of the two, we find in man 
a member adapted for the prehension and holding of objects, for 
climbing and for more or less suspending the body; while in 
the horse it is used essentially for weight bearing, supporting 
fifty-five per cent. of the body weight, and plays a fundamental 
part in the process of locomotion. In man it is rigidly attached 
to the thorax by means of the clavicle, while its sole attachment 
in the horse is by means of powerful and elastic muscles, with the 
heavy skin covering, which permits extensive movements of the 
member upon the chest. 
The scapulo-humeral articulation of man, with the support 
of the clavicle, stands out prominently from the thorax with 
the humerus free and the joint so formed that a very extensive 
area of motion, representing a hemisphere, is permitted. In the 
horse, on the other hand, the extensive flattened contour of the 
scapulo-humeral region with the angle existing between the two 
bones closely applied against the chest walls, prohibits in a large 
degree rotation, adduction, and abduction, and limits its move- 
ments in health chiefly to antero-posterior flexion and extension, 
so that direct strain upon the ligaments, originating in the 
humerus itself, is practically prohibited, while strain upon the 
joint transmitted through the radius is usually nullified by the 
free movement of the shoulder on the chest wall or by closure 
of the scapulo-humeral angle, each of which safeguards are denied 
to man. 
As a result of the formation of the shoulder man suffers 
rather frequently from severe strain or dislocation of that joint 
or fracture of the clavicle from violent impact on the humerus, 
while in the horse these accidents are rarely diagnosable, the dis- 
location of the scapulo-humeral articulation occurring so rarely 
that few practitioners see cases. Since dislocation must always 
constitute the finality of the strain of articular ligaments, its 
frequency serves as an index of the occurrence of the latter. 
Examining the limb as a whole, we find that in man it is 
capable of extension in a straight line from end to end, resulting 
