362 
LECTURES ON HORSES. 
revolving sweep, and the more free and loose the action of the 
shoulder, as will appear evident from the following diagram : — 
Taking the graduated quadrant A B to represent the arc the 
scapula describes in its imperfect revolution, it is manifest that, 
setting the limit of its motion forward as the figure 1, its sphere of 
revolution will be increased in proportion as its inclination or 
obliquity is greater at the commencement : a scapula whose base 
inclines to the figure 7 in the scale will have two degrees of ex- 
tent of action more than one which only reaches the figure 5, and 
two less than one whose base descends so low as the 9th degree. 
The first movements of the shoulder-bones, those that lift the 
limb off the ground and advance it, consist in a limited revolution 
of the scapula, in which its base turns backward and downward, 
its apex forward and upward, and in a simultaneous flexion and 
elevation of the humerus, the effect of which is to diminish the 
distance (represented in the jig. by the dotted line E) between it 
and the scapula. The projection of the limb in front of the body 
is effected by an extension of the humerus on the scapula, and, 
in rapid or forced movements, by an advance (not a revolution) of 
the scapula as well: but the instant the foot is grounded and 
becomes a fixed point and fulcrum, the scapula commences a 
counter-revolution, its base moving forward and upward, its apex 
backward and downward, and the humerus returns to its original 
semi-flexed position. Whether the limb moves upon the body, the 
foot being off the ground, or the body moves upon the limb, the 
foot being on the ground, in either case the scapula is in motion, 
its revolution, in regard to its summit, being backward and down- 
ward in one case, forward and upward in the other. 
The length, as well as the obliquity, of the scapula will have 
