MUSCULAR SYSTEM. 159 



flattened one that runs in front of it, and indeed forms quite a 

 sheath for it. Having emerged from its sheath, however, it spHts 

 into two divisions, which are left with only cellular coverings. 



Action. — To flex the hock ; in doing which it will have a ten- 

 dency to turn the joint inwards. 



2.— SUPERFICIAL POSTERIOR FEINIORO-CRURAL REGION. 



The muscles contained in this region are all affixed to the 

 OS calcis, and thereby become extensors of the hock : one of 

 them is continued afterwards down the leg, to be fixed both to 

 the fetlock and pastern, and hence operates as a flexor of those 

 parts at the same time. 



GASTROCNEMIUS EXTERN US. — Bifemoro-calcancus . 



Situation. — Superficial ; along the posterior part of the leg. 



Figure. — Elongated : flattened from before backwards ; broad, 

 thick, and bifurcated, superiorly; united and cordiform, inferiorly. 



Attachment. — Superiorly, to a roughened hollow just above 

 the external condyle of the os femoris, to the inner condyle, and 

 to a ridge extending from it : inferiorly, to the point of the 

 OS calcis. 



Relations. — Posteriorly, with the faschia and skin; anteriorly, 

 with the condyles of the femur, gastrocnemius and plantaris, 

 muscles of the deep posterior crural region, and the popliteal 

 bloodvessels and nerves; externally, with the biceps; internally, 

 with the adductor magnus and adductor tibialis. 



Direction, — Downward and backward. 



Structure. — The superior and middle parts are bulky, and con- 

 sist principally of a fleshy belly, bifurcate, whose surfaces are 

 partially covered by aponeurosis, discovering inferiorly a few 

 tendinous intersections. A little below the back of the stifle, the 

 bifurcations unite and form one entire fleshy belly, glistening in 

 many parts with tendinous fibres. Midway between the hock 

 and stifle the belly ends in a flattened tendon, partially divisible 

 into two or three portions, and decussates with the tendon of the 

 gastrocnemius internus, by which at the hock it is completely 

 enveloped. 



Action. — To extend the hock. 



GASTROCNEMIUS INTERNUS. — Fcmoro-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. 



Attachnie)it. — Superiorly, to the upper part of the roughened 

 hollow upon the back of the os femoris, above its external con- 



