The semitendinosns and sartorius muscles are also rotators inwards at the knee-joint.
II. The extensor of the knee-joint is properly one muscle, but divisible into four parts. It occupies the whole front and sides of the thigh. One distinct part is the rectus, or straight muscle, marked s on the Plate (fig. 3), which passes from the hip-bone straight down the front of the thigh till it ends in a broad, flat tendon, inserted into the upper sur face of the knee•pan.
The lower edge of the knee-pan has another ligament which passes down to be inserted in front of the shill-bone, so that the rectus muscle is practically attached to the front of the tibia. The rectus is supported on each side by an ex tensive sheet of muscle, which is inserted into the same tendon, 12 of Plate (fig. 3). When this large extensor muscle acts from its attach ment to the hip, it straightens the leg 'by ex tending the knee-joint. When the knee-joint is extended and fixed, the contraction of the muscle will flex the hip, that is, bend the trunk forwards.
Muscles of the Leg and the fore-leg the space between the shin and clasp bones in front of the leg is occupied by muscles which extend the foot. There is the long ex tensor of the toes, whose tendon runs over the back of the foot in four slips, one for each of the four outer toes. The tendon for the great toe is derived from a special muscle placed on the leg close to the long extensor. There is it third muscle (the anterior tibial) lying close against the tibia, whose tendon turns over the back of the foot at the instep to be inserted into the internal of the wedge-shaped bones of the tarsus. This is the muscle which raises the inner side of the foot, and spasm of which produces one form of clubfoot. On the outer side of the leg is another muscle (the third peroneal), whose muscle turns over the out side of the foot in a manner similar to the fore going. It raises the outer side of the foot ; and spasm of it produces a second variety of club-foot.
On the outer aspect of the leg are two muscles (the long and short peroneal), whose tendons pass behind the external malleolus to be inserted, the former into the base of the metatarsal bone of the great toe, and the latter into the metatarsal bone of the little toe. They extend the foot and give it an outward direc tion, while they strengthen the arch of the foot.
On the back of the foot is the short extensor of the toes, whose tendons, one to each of die four inner toes, join those of the long extensor.
The arrangement of the extensor tendons of the toes is exactly similar to the arrangement of those of the fingers.
On the back of the leg there are two large muscles, gastrocnemius (Pl. X., jig. 1, 25) and soleus, which form the bulk of the calf of the leg. The former is the larger, and arises from the condylea of the thigh-bone; the latter is be neath it, and arises from the heads of tibia and fibula. Both are united in a common tendon,
the thickest and strongest in the body, the tendo Achillis, so called from the old Greek fable, according to which Achilles was dipped by his mother into the River Styx, and so made invulnerable. He :las held by this tendon, which, therefore, did not get immersed, and so remained capable of being wounded, the only vulnerable part of his body ; and here he was in the end fatally wounded. The tendo Achillis is inserted into the back part of the projec tion of the heel-bone, the os calcis (Fig. 73). The two muscles, acting through the tendon, pull up the heel, and so raise the body on the toes.
They are used in walking, jumping, &c. Beneath the calf muscles are the long flexor of the toes and the special flexor muscle of the great roe. The tendons pass behind the internal malleolus —the inner projection of the tibia at the ankle joint—to reach the sole of the foot, where the long flexor divides into four slips, one for the end bone of each of the four outer toes. The tendon of the special flexor of the great toe proceeds to the last phalanx of that toe. In the sole of the foot itself is the short flexor of the toes. It arises from the heel-bone, and has four tendons, one for the second phalanx of each of the four outer toes. The tendons of the long flexor, in their passage to the last phalanges, pierce those of the short flexor. At the back of the leg, between the two bones, is the posterior tibial muscle, whose tendon passes beneath the internal malleolus to reach the scaphoid bone, to which it is attached. It extends the foot and gives it an inward direction. In the sole of the foot there are special muscles for bending, and directing outwards or inwards the great toe, and for bending and abducting the toe, as in the band for the thumb and little finger.
Besides, there are interossei muscles, also, as in the hand, running between the metatansal bones, arranged for moving the toes to one side or another.
In the sole of the foot a strong fibrous tissue, the plantar fascia, covers the muscles and extends from the heel-bone forward to the toes. It has a central and two side portions, the central portion being separated from the side portions by fibrous partitions which sink between the muscles deeply into the sole of the foot. When abscesses occur in the sole of the foot the plantar fascia confines the matter that is formed, and thus prevents it spreading. At the same time it prevents it working its way to the sur face, so firmly does the fascia bind down the tissue. For this reason abscesses in the foot are often very troublesome to deal with, and very painful.