514 
ANATOMY OF THE HORSE. 
and expanding' in breadth towards its termination: it passes, at 
the knee, under the anterior annular ligament, within a synovial 
sheath, furnished with a bursa mucosa. 
. Action .—To extend the leg. 
extensor pedis. — Epitrochlo-prephalangeus. 
Situation .—Fore and outer part of the arm. 
Form .—Elongated ; pyramidal: more flattened than, but not 
so thick as the preceding muscle. 
Attachment .—Superiorly, to the fore part of the external con¬ 
dyle of the humerus, to the outer part of the head and supero- 
external part of the body of the radius, and also to the capsular 
ligament of the elbow joint: inferiorly, to the front parts of the 
lower end of the os suffraginis, the os coronoe, and the coronal 
[ )rocess of the os pedis; adhering in its course to the capsular 
igament of the fetlock joint. 
Relations. —Anteriorly, with the faschia and skin: posteriorly, 
with the extensor obliquus and the radius: internally, with the 
preceding muscle: postero-externally, w ith the extensor suffragi¬ 
nis. Behind it, between the bone and it, run branches from the 
spiral artery and nerve. 
Structure. —The superior attachment is both tendinous and 
fleshy: that portion w hich is attached to the radius consists of a 
broad, thin, pale, fleshy fasciculus, running to unite itself to the 
main body of the muscle. It has but one or two, and those but 
partial, tendinous intersections. Its surfaces are aponeurotic. It 
becomes a single tendon nearly about the same place as the for¬ 
mer muscle; but the tendon is smaller. It pursues its course 
under the annular ligament, through a cellular sheath furnished 
with a bursa; and continues dow n the leg, closely attached by 
cellular membrane to the cannon bone, broadening somewhat 
in its course, but w idely expanding after it has passed over the 
fetlock; and in its expansion so completely covering and ad¬ 
hering to the pastern joints, that it seems to them, in front, to 
serve the purpose of capsular ligament. 
Action .—To extend the foot and pasterns; and at the same 
time to assist in the extension of the knee. 
extensor suffraginis. — Radialis-prephalangeus . 
Situation .—Postero-external part of the arm. 
Form .—Narrow; thin ; elongated. 
Attachment .—Superiorly, to the postero-external and superior 
parts of the radius, and to the posterior (sharpened) border of 
the ulna: inferiorly, to the supero-anterior part of the os suffra¬ 
ginis, adhering to the capsular ligament of the fetlock joint. 
