308 THE MUSCULAR SYSTEM. 
muscle of the leg), and the plantaris; and (2) a deep set, consisting of the popliteus, 
flexor longus digitorum, tibialis posticus, and flexor longus hallucis. 
The gastrocnemius arises by two heads, inner and outer, by means of 
strong tendons (prolonged over the surface of the muscle) from the lateral surface 
of each condyle of the femur and from the back of the capsule of the knee-joint. 
A bursa lies beneath each tendon of origin. Each fleshy belly of the muscle is inserted 
into a broad membranous tendon, pro- 
7 
q 
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7, 
, 
/ longed upwards on its deep surface for 
PLANTARIS 
MUSCLE (cut) 
\ 
li 
POPLITEUS 
some distance. The inner head is the 
larger. 
The tendo Achillis is formed by the 
union of the two membranous inser- 
tions of the bellies of the gastrocnemius. 
SEMIMEMBRANOSUS 
TENDON (cut) 
MUSCLE Prolonged upwards beneath the separ- 
ate bellies, the tendon forms a broad 
membranous band connecting together 
the lower parts of the two_ bellies. 
Narrowing gradually, and becoming 
thicker in the lower half of -the leg, 
the tendon is finally inserted into the 
‘sorevs lower half of the posterior surface of 
wesete the os calcis. A bursa lies beneath the 
tendon at its insertion. The tendo 
Achillis also affords insertion to the 
soleus and (sometimes) the plantaris 
muscles. 
The gastrocnemius is superficial 
except at its origin. The inner head 
is concealed by the semitendinosus and 
selmimembranosus muscles, and covers 
partially the lower part of the popliteal 
vessels and the tibial nerve. It forms 
part of the inner boundary of the 
popliteal space. The outer head is 
concealed partially by the biceps tendon 
| _._ and the peroneal nerve, and covers the 
PERONEUS LONGUS : : 
plantaris muscle, the popliteal vessels, 
and the tibial nerve. It forms part of 
the outer boundary of the popliteal 
space. The two bellies are for the 
Hxternalanmular most part in close contact, the ex- 
Cotas ternal saphenous vein occupying the 
interval between them. The tendo 
Achillis in the lower half of the leg 
partially conceals the soleus and the 
deeper muscles. The plantaris tendon 
lies along its inner border. 
The plantaris arises from the ex- 
ternal supra-condyloid ridge of the 
femur for about an inch at its lower end, and from the posterior ligament of the 
knee-joint. It forms a narrow fleshy slip which ends in a tendon extending down 
the back of the leg, to be inserted into the tuberosity of the os calcis, or the tendo 
Achillis, or the internal annular ligament. The tendon of the muscle is capable 
of considerable lateral extension. The plantaris lies between the outer head of 
the gastrocnemius and the soleus, and crosses the popliteal vessels and the tibial 
nerve. In the lower half of the leg its tendon lies along the inner border of the 
tendo Achillis. The muscle is not always present. 
The soleus has a triple origin: (1) from the posterior surface of the head and 
the shaft of the fibula in its upper third; (2) from a fibrous arch stretching over 
Tibial nerve and 
popliteal vessels 
PLANTARIS TENDON 
(ent) 
Trenpo ACHILLIS 
ris 4 
Internal annular 
ligament 
Fic. 263.—THE SoLEus MUSCLE. 
oy 
