242 
ANATOMY OF THE HORSE. 
gastrocnemius internus. — Femoro-phalangeus . 
Situation .— Postero-mesian part of the leg. 
Form. —Cordiform; elongated; thicker in the middle than at 
the extremities. Its tendon, below the hock, is flattened, and 
upon the anterior surface excavated. 
Attachment .—Superiorly, to the upper part of the roughened 
hollow upon the back of the os femoris, above its external con¬ 
dyle. Interiorly, it is continued over the hock, down the posterior 
part of the leg, to be fixed to the os eoronae. 
Relations .—Posteriorly, with the gastrocnemius externus and 
skin ; anteriorly, with the stifle joint, the muscles of the posterior 
deep crural region, tendons of the gastrocnemius externus and 
flexor perforans. The first crural nerve runs also along the front 
side. 
Peculiarities .—Remarkable for the little difference in volume 
there exists between the fleshy belly and its tendon; and in 
being entirely tendinous until it has descended to the stifle. 
Structure .—The belly of this muscle is of considerably less 
volume than that of the gastrocnemius externus ; but it has more 
tendon in its composition. About half way down the thigh it 
becomes entirely tendinous; and its tendon, which is flattened, 
turns round that of the gastrocnemius externus in approaching 
the hock: so that the relative position of the two muscles be¬ 
comes reversed in their tendons. In passing over the point of 
the hock the tendon expands into a sort of cap or theca , which 
is so fixed and closed in around its border, by cellular substance, 
to the bone that a complete ball-and-socket joint is formed be¬ 
tween them, circumscribed within the space of about an inch from 
its centre all the way round, and lined by a thin delicate mem¬ 
brane secreting synovia into the interspace. It constitutes, in 
fact, altogether, what is denominated a bursa muscosa ; but is 
one that, from its size and disposition to take on disease, pecu¬ 
liarly merits the attention of the anatomist. From this bursal 
formation it proceeds down the posterior part of the leg; and 
from the place at which it leaves the hock takes the name of 
tendo perforatus . Its subsequent course and attachment, to¬ 
gether with its relations to the tendo perforans , answer to the 
descriptions given of the tendons of the same name in the fore 
extremity. 
Action .—To extend the hock: but to flex the fetlock and 
pastern. 
plantaris. — Peroneo-calcaneus. 
Situation .—Postero-external part of the thigh. 
Form.— Elongated ; thin ; slender. 
