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The Muscles on the Posterior Aspect of the Leg.
The muscles on the back of the leg are divisible into two groups, superficial and deep.
MEDIAL HEAD OF
The superficial group comprises the gastrocnemius and soleus (constituting together the triceps sure) and the plantaris. They form the prominence of the calf of the leg. The gastrocnemius
is superficial except at
LATERAL HEAD OF its origin, where the
PERON EUS BREVIS
two bellies, forming the
liteal fossa, are over- Semimem-
FLEXOR DIGITORUM means of strong tendons which are prolonged over the surface of the muscle. The lateral head arises from an impression on the proximal and posterior part of the lateral surface of the lateral condyle of the femur, and from the distal end of the lateral epicondylic line; while the medial head arises from prominent rough mark on the popliteal surface of the femur, proximal to the medial epicondyle and posterior to the adductor tubercle. Each head has an additional origin from the back of the capsule of the knee-joint. A
FIG. 383. THE DEEP MUSCLES ON THE
BACK OF THE RIGHT LEG.
Each fleshy belly
TO THE POSTERIOR SURFACE OF THE RIGHT TIBIA.
of the muscle is inserted, separately, into a broad membranous tendon, prolonged proximally on its deep surface for some distance. The medial head is the larger. The tendo calcaneus is formed by the union of the two membranous insertions
of the bellies of the gastrocnemius. Prolonged proximally beneath the separate , bellies, the tendon forms a broad membranous band connecting together the distal parts of the two bellies.
Narrowing gradually, and becoming thicker in the distal half of the leg, the tendon is finally inserted into the posterior aspect of the calcaneus. A bursa lies deep to the tendon at its insertion. The tendo calcaneus also affords insertion to the soleus and (sometimes) the plantaris muscles.
Nerve-Supply. Each head of the muscle is innervated by a branch from the tibial nerve (S. 1. 2.).
Actions. The muscle is a powerful flexor of the knee and extensor of the ankle.
M. Plantaris. The plantaris arises by fleshy fibres from the lateral epicondylic line of the femur for about an inch at its distal end, from the adjacent part of the popliteal surface of the femur, and from the oblique ligament of the knee-joint.
It forms a narrow fleshy slip which ends in a tendon that extends distally in the back of the leg, to be inserted into, the medial side of the tuberosity of the calcaneus, or the tendo calcaneus, or the ligamentum laciniatum. The tendon of the muscle is capable of considerable lateral extension.
The plantaris lies between the lateral head of the gastrocnemius and the soleus. In the distal half of the leg its tendon lies along the medial border of the tendo calcaneus. The muscle is not always present.
Nerve-Supply.-Tibial nerve (L. 4. 5. S. 1.).
Actions. The muscle is an accessory flexor of the knee and extensor of the ankle.
M. Soleus. The soleus has a triple origin from (1) the posterior surfaces of the head and the proximal third of the body of the fibula; (2) a fibrous arch (arcus tendineus m. solei) stretching, over the popliteal vessels and tibial nerve, between the tibia and fibula; and (3) the oblique line, and the middle third of the medial border of the tibia (Fig. 384, p. 428).
From their origin the proximal muscular fibres are directed distally to join a tendon, placed on the superficial aspect of the muscle, which is inserted into the tendo calcaneus; the more distal fibres are inserted directly into the tendo calcaneus to within one or two inches of the calcaneus.
Nerve-Supply. Two nerves supply this muscle. One from the tibial nerve in the popliteal space enters its superficial surface (S. 1. 2.); the other from the tibial nerve in the back of the leg supplies the deep surface of the muscle (L. 5. S. 1. 2.).
Actions. The soleus is a powerful extensor of the ankle.
The deep muscles of the back of the leg comprise the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior.
The popliteus muscle is deeply placed behind the knee-joint, in the floor of the popliteal fossa, and is covered by the popliteal vessels and tibial nerve. The flexor digitorum longus lies behind the tibia, the flexor hallucis longus behind the fibula, and the tibialis posterior, lying between them, is related to the interosseous membrane and both bones of the leg. All these muscles are concealed by the superficial group, and are bound down to the bones of the leg by layers of the deep fascia.
M. Popliteus. The popliteus arises, by a stout tendon, from a rough impression in front of a groove on the lateral aspect of the lateral epicondyle of the femur. The tendon passes between the lateral meniscus and the capsule of the knee-joint, and pierces the posterior ligament, from which it takes an additional fleshy origin. A bursa is placed on the medial side of the tendon, and it usually communicates with the synovial cavity of the knee-joint.
The muscle is inserted, by fleshy fibres, (1) into a triangular surface on the back of the tibia above the oblique line (Fig. 384, p. 428), and (2) into the fascia over it (the popliteus fascia, derived from the tendon of the semimembranosus muscle).
The popliteus minor is a small occasional muscle attached to the popliteal surface of the femur and the posterior ligament of the knee-joint.
Nerve-Supply. The popliteus is supplied by a branch of the tibial nerve (L. 4. 5. S. 1.), which winds round the distal border of the muscle and enters it in its deep surface. Actions.-A medial rotator of the tibia and flexor of the knee.
M. Flexor Digitorum Longus.-The flexor digitorum longus lies in both the back of the leg and the sole of the foot. Its origin is, by fleshy fibres, from the posterior surface of the body of the tibia in its middle three-fifths, distal to the oblique line, and medial to the vertical line and the origin of the tibialis posterior from the fascia over it, and from an intermuscular septum on each side (Fig. 384, p. 428).
Its tendon, after crossing obliquely over the tendon of the tibialis posterior, passes deep to the ligamentum laciniatum, invested in a special mucous sheath, and enters the sole of the foot. There it crosses superficially the tendon of the flexor hallucis longus, and finally divides into four subordinate tendons, which are inserted into the four lateral toes in precisely the same manner as the flexor digitorum profundus is inserted in the hand (p. 389). Each tendon enters the digital sheath of the toe, perforates the tendon of the flexor digitorum brevis, and is inserted into the base of the terminal phalanx. Vincula accessoria (longa and brevia) are present as in the hand.
The tendon of the flexor hallucis longus sends a fibrous band to the tendon of the flexor digitorum longus as it crosses it in the sole of the foot; the band usually passes to the tendons destined for the second and third toes. Associated with this muscle in the sole of the foot are the lumbricales and quadratus plantæ muscles.
Mm. Lumbricales.-The lumbricales are four small muscles which arise in association with the tendons of the flexor digitorum longus in the sole. The first muscle arises by a single origin from the tibial side of the tendon of the flexor digitorum longus for the second toe; each of the other three arises by two heads from the adjacent sides of two tendons.
Each muscle is inserted into the dorsal expansion of the extensor FIG. 385.—THE MUSCLES OF THE RIGHT FOOT (Second Layer), tendon, the metatarso-phalangeal capsule, and the base of the first phalanx, precisely as in the case of the lumbrical muscles of the hand. Each muscle passes forwards on the tibial side of the corresponding toe, superficial to the transverse metatarsal ligament.
Nerve-Supply. The flexor digitorum longus is supplied by the tibial nerve (L. 5. S. 1.). The first lumbrical is supplied by the medial plantar nerve (L. 4. 5. S. 1.); the other three, by the lateral plantar nerve (S. 1. 2.).
Actions. The flexor digitorum longus extends the ankles and flexes the four lateral toes.
The lumbrical muscles have a similar action to those of the hand; they flex the metatarsophalangeal, and extend the interphalangeal joints of the four lateral toes.
M.Quadratus Plantæ. The quadratus plantæ (O.T. accessorius) arises by two heads: (1) the lateral tendinous head springs from the lateral border of the plantar surface of the calcaneus and from the lateral border of the long plantar ligament; (2) the medial head, which is fleshy, arises from the concave medial surface of the calcaneus in its whole extent, and from the medial border of the long plantar ligament (Fig. 379, p. 425). The long plantar ligament separates the two origins. The two heads unite to form a flattened band, which is inserted into the dorsal aspects of the tendons of the flexor digitorum longus, and usually into those destined for the second, third, and fourth toes.
In the sole of the foot the tendons of the flexor digitorum longus, along with the lumbricales and quadratus plantæ, and the flexor hallucis longus muscles, constitute the second layer of muscles, lying between the abductors of the great and little toes and the flexor digitorum brevis superficially, and the flexor brevis and adductor of the great toe more deeply.
Nerve-Supply. Lateral plantar nerve (S. 1. 2.).
Actions. The muscle is an accessory flexor of the toes, assisting the long flexor of the toes. It tends to draw the tendons into which it is inserted into the middle of the sole of the foot.
M. Flexor Hallucis Longus.-The flexor hallucis longus arises, on the back of the leg, between the tibialis posterior and the peronæi muscles, from the distal two-thirds of the posterior surface of the body of the fibula, from the fascia over it, and from intermuscular septa on either side.
Its tendon passes deep to the ligamentum laciniatum, enclosed in a special mucous sheath, and after grooving the posterior surface of the distal end of the tibia, the talus, and the plantar surface of the sustentaculum tali of the calcaneus, it is directed forwards in the sole of the foot, to be inserted into the base of the terminal phalanx of the great toe.
In the foot it crosses over the deep aspect of the tendon of the flexor digitorum longus, and gives to it a strong fibrous slip, which is prolonged into the tendons for the second and third toes.
Nerve-Supply. Tibial nerve (L. 5. S. 1. 2.).
Actions. The muscle is one of the most important in the leg and foot. It is an extensor of the ankle and a flexor of the great toe. By its position in relation to the tarsus and inferior calcaneo-navicular ligament, it has an important share in maintaining and supporting the arch
of the foot.
M. Tibialis Posterior.-The tibialis posterior has a fourfold fleshy origin in the leg. It arises (1) from the proximal four-fifths of the medial surface of the body of the fibula between the medial crest and the interosseous crest; (2) from the distal part of the lateral condyle, and from the proximal two-thirds of the body of the tibia, distal to the oblique line and between the vertical line and the interosseous border (Fig. 384, p. 428); (3) from the interosseous membrane; and (4) from the fascia over it and the septa on either side. The muscle gives rise to a strong tendon which passes deep to the ligamentum laciniatum, invested by a special mucous sheath, and grooves the back of the medial malleolus, on its way to the medial border of the foot.
After crossing over the plantar calcaneo-navicular ligament between the sustentaculum tali and the navicular bone, the tendon spreads out and is inserted by three bands into (1) the tubercle of the navicular bone and the plantar surfaces of the first and second cuneiform bones, (2) the plantar aspects of the bases of the second, third, fourth, and sometimes the fifth metatarsal bones, the second and third cuneiform bones, and the groove on the cuboid, and (3) into the medial border of the sustentaculum tali of the calcaneus (Fig. 379, p. 425).
The peronæo-calcaneus muscle, when present, arises from the fibula, and is inserted into the calcaneus.
Nerve-Supply.-Tibial nerve (L. 5. S. 1.).
Actions. The muscle extends the ankle and inverts the foot.