PLANTARIS 485 



sublimis of the forearm. In many of the monkeys and in the prosimians the plantaris is much 

 more developed than in man. 



The gastrocnemius (fig. 413).^ — Medial head. — Origin. — From a facet on the back of the 

 medial condyle of the femur above the articular surface, from an area on the back of the femur 

 superior and lateral to this, and from the femoral margin of the capsule of the knee-joint. 

 Lateral head. — Origin. — From a facet on the proximal portion of the postero-lateral surface 

 of the lateral condyle of the femur and from a rough area situated more medially and at a 

 greater distance from the joint. 



Structure and insertion. — The heads of the gastrocnemius are similar in structure. From the 

 condylar facets there descend aponeurotic bands, one on the medial margin and the medial side 

 of the posterior surface of the medial head, the other on the lateral margin and the lateral side 

 of the posterior surface of the lateral head. These bands descend about two-thirds of the way 

 down the muscle. In the tendon of the lateral head a sesamoid bone is frequently found. The 

 fibre-bundles of the muscle pass obliquely from the supracondylar areas of origin and from the 

 deep surface of the aponeurosis on each side to the tendon of insertion. This tendon begins as 

 a septum between the two heads, and as a lamina on the deep surface of each head. The septum 

 and laminae soon fuse with the broad aponeurosis which covers the dorsal surface of the soleus. 

 The attachment of fibre-bundles continues to about the middle of the back of the leg. The 

 attachment of the medial head extends more distally than that of the lateral head. As a rule, 

 the medial head is also the broader and thicker of the two. 



The soleus. — Origin. — (1) By a fibular head from the back of the head and the proximal 

 third of the posterior surface of the shaft of the fibula, and from the intermuscular septum 

 between it and the peroneus longus; and (2) by a tibial head from the transverse septum over the 

 distal margin of the pophteus, from the pophteal line, and from the middle third of the medial 

 border of the tibia. 



Structure and insertion. — From the fibular and tibial origins arise broad aponeuroses which 

 unite proximally on the deep surface of the muscle so as to form a fibrous arch over the pos- 

 terior tibial vessels and nerves. Distally they diverge and become more narrow, but the fibular 

 aponeurosis is continued on the fibular side and the tibial aponeurosis on the tibial side of 

 the muscle as far as the distal quarter of the leg. The main portion of the belly of the muscle 

 is formed by fibre-bundles which arise from the posterior surface of these aponeuroses and 

 pass obliquely to be inserted in a bipenniform manner on the deep surface of the tendon of 

 AchUles. This tendon begins as a broad aponeurosis which covers the greater part of the 

 posterior surface of the muscle, and gradually converges into a heavy fibrous band that is in- 

 serted into the calcaneus. The bundles of fibres of the tendon take a slightly spiral course. 

 Those on the posterior surface run from the medial margin toward the lateral surface of the 

 calcaneus; those on the anterior surface in a reverse direction. The attachment of the fibre- 

 bundles continues to within a short distance of the heel. A few of the fibre-bundles arise 

 directly from the fibula and the posterior intermuscular septum. On the deep surface of the 

 belly of the muscle there is an accessory fasciculus which is formed by fibre-bundles that spring 

 on each side from the anterior surface of the aponeuroses of origin of the muscle and have a 

 bipenniform insertion on each side of a thin, obhque tendinous lamina which inferiorly becomes 

 united to the deep surface of the tendon of Achilles. 



The plantaris (fig. 413). — This muscle arises from the distal part of the lateral line of 

 bifurcation of the hnea aspera, in close association with the lateral head of the gastrocnemius. 

 The fibre-bundles give rise to a flat, short, fusiform belly, and are united to a narrow tendon 

 which extends along the medial edge of the tendon of Achilles to the lateral part of the dorsal 

 surface of the calcaneus, where it terminates in the neighbouring fibrous tissue. 



Nerve-supply. — From the tibial (internal pophteal) part of the sciatic nerve in the popliteal 

 space nerves arise for each head of the gastrocnemius. Each nerve enters the middle third of the 

 deep surface of the head near the proximal margin. The nerve-supply for the soleus is from two 

 sources. One nerve arises in the popliteal space, often in company with the nerve to the lateral 

 head of the gastrocnemius. It enters the posterior surface of the muscle near the proximal 

 border and divides into two branches, one for each head of the muscle. The tibial (posterior 

 tibial) nerve gives rise to a branch which, about half-way down the leg, enters the deep surface 

 of the muscle and furnishes branches for the deep portion of the muscle on each side. The 

 nerve-supply of the plantaris is by a branch from the tibial (internal pophteal) portion of 

 the sciatic. This arises in the popliteal space and enters the deep surface of the muscle. 



Relations. — The semimembranosus winds about the medial margin of the medial head of 

 the gastrocnemius to its deep surface. The biceps passes to the lateral side of the lateral head 

 of the gastrocnemius, and the plantaris along its medial margin. The semimembranosus and 

 biceps above, the medial head of the gastrocnemius and the plantaris below, bound the pouhteal 

 space. The peroneal (external popliteal) nerve passes from the popliteal space obliquely across 

 the plantaris and the lateral head of the gastrocnemius. The medial sural (short saphenous) 

 nerve and the small saphenous vein pass between the heads of the gastrocnemius to the surface 

 and thence to the lateral side of the ankle. From the peroneal (external popliteal) nerve in the 

 popliteal space the lateral sural (communicans peronei) nerve extends distally over the calf. 

 The (posterior) tibial nerve and posterior tibial artery and vein run between the two heads of the 

 gastrocnemius, and then beneath the soleus to the medial side of the ankle. In the region of the 

 tendon of Achilles a considerable space filled with fatty tissue intervenes between the tendon 

 and the transverse septum. 



Action. — The contraction of the triceps surse produces extension, adduction, and inversion 

 of the foot. The gastrocnemius is also a flexor of the leg. The plantaris has no known function 

 in man. In some animals it is an extensor of the plantar fascia. 



Variations. — There is considerable variation in the extent of the separation of the different 

 parts of the triceps sura>. The tendons of the three heads may be separate nearlj' to the heel. 

 Either or both heads of the gastrocnemius or the soleus may be doubled. A sHp from the biceps 



