AND LEG OF THE HORSE. 
563 
ances and that of their progeny, it were ascertained how many 
years the latter endured before they were taken, or rather com¬ 
pelled to be taken, out of training. 
The Tendons ,—We have before observed, that there are no 
muscles situated below the knee; if there were, the leg, instead of 
being light and active, would be heavy and unwieldy as that of an 
elephant. A pound of substance at the fetlock would require more 
power to move it than four pounds placed above the knee. 
Accordingly, we find that the muscles, both those which ex¬ 
tend and those which flex the limb, are placed above the knee, and 
communicate motion to the foot by means of the long flexor and 
extensor tendons. This being the case, it must be evident that 
the most onerous duty, viz., that of raising the leg, is performed by 
the flexors, and accordingly we find that they are more than three 
times the size of the extensors. There seems, however, to be a 
greater disproportion between the tendons than between their cor¬ 
responding muscles, which we must explain by observing, that the 
flexors, beside their principal use in progression, also contribute 
greatly to the support of the leg. The animal, in a measure, stands 
upon his flexor tendons, which is shewn by dividing them, when 
the fetlock joints immediately become more oblique. To effect 
this function both sinews are expanded at the fetlock, and the per- 
forans also at the back of the os coronse, and again still more at the 
navicular joint. 
We have before observed, that the perforatus forms a sheath for 
the perforans, at and below the fetlock joint, thus affording a beau¬ 
tiful mechanical contrivance, for a sheath could not be dispensed 
with, and yet no material could be spared for the purpose, lightness 
being so great an object. Accordingly, the difficulty is at once re¬ 
moved by the smaller tendon forming a sheath for the larger, by 
which, without any increase of bulk, the tendons are enabled to act 
jointly or severally as may be required. 
*^In the operation which we shall afterwards speak of—the division 
of the flexor tendons—the act of healing unites both tendons together 
by the intermediate substance that grows between them; the effect 
of which is, that the two sinews can afterwards only act together. 
The perforans can no longer slide through the perforatus, but the 
action of the latter so limits that of the former, that the horse can 
no longer flex the coffin bone on the os coronae. The flexor per¬ 
forans, after emerging from its sheath, expands considerably, and 
enters a joint capsule, which occupies the whole of the back part of 
the os coronae, and in which the tendon and the bone are closely 
adapted to each other, the former resting on the latter, and this re¬ 
posing on the soft elastic heels, which yield in every direction, thus 
forming one of the most elastic springs in the whole body. After 
