364 THE MUSCLES 



2. SEMI-TENDINOSUS 



The semi-tendinosus (fig. 288) — named from the long tendon Avhidi forms 

 the lower half of the muscle — is fusiform and somewhat flattened. 



Origin. — By a tendon which is common to it and the preceding muscle, from 

 the lower and inner of the facets at the back of the tuber ischii. 



Insertion. — (1) The upper part of the inner surface of the tibia Ijelow and 

 l)t"hind the insertion of the gracilis; (2) the deep fascia of the inner side of the leg. 



Structure. — The rounded and somewhat flattened tendon of aliout two inches 

 (.5 cm.) in length is succeeded by a fusiform mass of muscular filtres, wliich end 

 just below the middle of the thigh in a flattened cylindrical tendon. This runs 

 directly downwards along the inner side of the i)opliteal space, Avhere it can easily 

 be felt beneath the skin, behind and external to the tendon of the gracilis, in com- 

 pany with which it passes downwards and forwards behind the internal condyle to 

 its insertion below the inner tuberosity. From the lower border of the flattened 

 tendon an aponeurosis passes downwards to the deep fascia of the leg. The fleshy 

 part of the muscle is crossed about its middle by a thin tendinous intersection 

 running downwards and outwards. 



Nerve-supply. — From the first, second, and third nerves of the sacral plexus 

 by means of l)ranches from the great sciatic nerve which enter the outer i»art of 

 the deep surface of the muscle two or three inches (about 6 cm. ) l)elow the tulier 

 ischii. 



Action. — To extend the hip and flex the knee, and when the knee is flexed to 

 rotate the leg inwards. Acting from below, it lifts up the body from the stooping 

 position. 



Relations. — Behind, the gluteus maximus and fascia lata; on its outer side the 

 biceps; in front, the semi-meml^ranosus, adductor magnus, and near the knee the 

 gracilis, sartorius, and the inner head of the gastrocnemius. The large Inirsa 

 beneath the sartorius tendon also Avraps round the lower part of the tendon of the 

 semi-tendinosus, and separates it from the internal lateral ligament of the knee- 

 joint. 



3. SEMI-MEMBRANOSUS 



The semi-membranosus (fig. 288) — named from the broad membrane-like 

 aponeurosis which forms the upper third of the muscle — is strong, flattened, and 

 fusiform. 



Origin. — The anterior and upper of the facets upon the back of the tuljer ischii. 



Insertion. — (1) The lower part of the jiosterior extremity of the groove upon 

 the l)ack and inner side of the inner tuberosity of the til)ia; (2) by a band of filires 

 which pass upwards and outwards to the upper and back part of the external 

 condyle of the femur, and blend with the posterior ligament of the knee-joint; (3) 

 by a broad expansion which, passing dowuAvards and outwards from its insertion 

 into the inner tuberosity to the oblique line at the back of the tibia, forms the 

 aponeurosis which invests the posterior surface of the popliteus; (4) a few fibres 

 pass downwards and forwards from the lower liorder of its tiljial insertion to lilend 

 with the internal lateral ligament. 



Structure. — Tlie upper part of the muscle consists of a strong flat tendon about 

 three-ijuarters of an inch (nearly 2 cm.) Ijroad, which extends along the outer 

 })order of the muscle to the middle of the thigh. The tendon of insertion is not 

 quite so l)road luit nmch thicker, and reaches upon the inner border of the nniscle 

 also as high as the middle of the thigh. Between these two tendons the nuiscular 

 fibres which are comparatively short pass downwards and inwards, Ix'ginning 

 upon the upper tendon about four inches (10 cm.) below the tuber ischii, and 

 ending upon the lower tendon close to the upper part of the inner condyle. The 

 nuiscle has therefore a very distinctly penniform arrangement, but it is peculiar in 

 this respect that the fleshy filires are at each extremity attached to a tendon, and 

 are not, as is usually tlie case, at one extremity attaclied to the bone. It is also 

 unusual for a muscle to have so long a tendon at its i)roximal end. One effo'ct of 



