308 
JSCTURF.S ON HORSES. 
also, to a considerable extent, make it perform a sort of rotatory 
motion : all which, the latter especially, he is enabled to do in 
consequence of the mobility existing in the joint forward between 
the ball or head of the humerus and the socket in the lower end 
of the scapula. 
The power of throwing the leg outwards or inwards in action, of 
turning the toe out or in, of performing those motions in the manege 
called passaging or shouldering -in, all resides in the rotatory mo- 
tion possessed by this joint. 
Viewing the relative positions of the bones of the fore-limb in 
the standing posture, we perceive that the two composing the 
shoulder constitute, in situ, an angle of an obtuse character, hav- 
ing two sides ; a superior, formed by the scapula ; an inferior and 
shorter one, by the humerus : the point of the angle being turned 
forwards. This oblique or angular arrangement is attended with 
several manifest advantages. A larger extent of surface upon the 
side of the body is occupied and embraced by the bones so dis- 
posed, thus affording more extensive and firmer attachment of the 
limb to the trunk. At the same time that this angular apposition 
better ensures their connexion with the ribs, it likewise affords the 
bones facility of motion upon each other, without risk of disseve- 
ration or detachment from the sides of the chest ; for the move- 
ments of the shoulders, which in action are considerable, have to 
be carried on, not only while the foot is off the ground, but at a 
time when all the weight of the body is imposed upon them. 
Another advantage of the angle is the extensive bordering and 
powerful leverage offered for the attachment and operation of 
muscle. Had the bones of the shoulder been placed upright or 
perpendicularly, one upon the other, in the first place, they could 
not have been made any thing like their present length; in the 
second, their connexion with the body would not have been 
equally secure; and, in the third place, their movements upon 
each other must have been comparatively restricted, giving rise 
to something in the form of action in the fore-limbs a great deal 
worse than that paddling sort of going which we denominate 
‘‘pinned in the shoulders.” This will appear more intelligible 
after we have shewn what is the nature of the motions or action 
of the shoulders. 
[To be continued.] 
