340 MUSCLES AXD FASCIAE. 



By its deep surface, with the Semi-membranosus, Adductor magnus, inner liead of 

 the Gastrocnemius, and internal lateral ligament of the knee-joint. 



The Semi-membranosus, so called from the membranous expansion on its anterior 

 and posterior surfaces, is situated at the back part and inner side of the thigh. 

 It arises by a thick tendon from the upper and outer part of the tuberosity of the 

 ischium, above and to the outer side of the Biceps and Semi-tendinosus, and is 

 inserted into the inner and back part of the inner tuberosity of the tibia, beneath 

 the internal lateral ligament. The tendon of the muscle at its origin expands 

 into an aponeurosis, which covers the upper part of its anterior surface ; from this 

 aponeurosis muscular fibres arise, and converge to another aponeurosis, which 

 covers the lower part of its posterior surface, and this contracts into the tendon of 

 insertion. The tendon of the muscle at its insertion divides into three portions ; 

 the middle portion is the fasciculus of insertion into the back part of the inner 

 tuberosity, sending down an expansion to cover the Popliteus muscle. The 

 internal portion is horizontal, passing forwards beneath the internal lateral liga- 

 ment, to be inserted into a groove along the inner side of the internal tuberosity. 

 The posterior division passes upwards and backwards, to be inserted into the back 

 part of the outer condyle of the femur, forming the chief part of the posterior 

 ligament of the knee-joint. 



The tendons of the two preceding muscles, with those of the Gracilis and 

 Sartorius, form the inner ham-string. 



Relations. By its superficial surface, with the Semi-tendinosus, Biceps, and 

 fascia lata. By its deep surface, with the popliteal vessels, Adductor magnus ; 

 and the inner head of the Gastrocnemius, from which it is separated by a synovial 

 bursa. By its inner border, with the Gracilis. By its outer border, with the great 

 sciatic nerve, and its internal popliteal branch. 



Nerves. The muscles of this region are supplied by the great sciatic nerve. 



Actions. The three ham-string muscles flex the leg upon the thigh. When the 

 knee is semi-flexed, the Biceps, from its oblique direction downwards and outwards, 

 rotates the leg slightly outwards ; and the Semi-membranosus, in consequence of 

 its oblique direction, rotates the leg inwards, assisting the Popliteus. Taking 

 their fixed point from below, these muscles serve to support the pelvis upon the 

 head of the femur, and to draw the trunk directly backwards, as is seen in feats 

 of strength, when the body is thrown backwards in the form of an arch. 



Surgical Anatomy. The tendons of these muscles occasionally require subcutaneous division 

 in some forms of spurious anchylosis of the knee-joint, dependent upon permanent contraction 

 and rigidity of the Plexor muscles, or from stiffening of the ligamentous and other tissues sur- 

 rounding the joint, the result of disease. This is easily effected by putting the tendon upon the 

 stretch, and inserting a narrow sharp-pointed knife between it and the skin ; the cutting edge 

 being then turned towards the tendon, it should be divided, taking care that the wound in the 

 skin is not at the same time enlarged. This operation has been attended with considerable suc- 

 cess in some cases of stiffened knee from rheumatism, gradual extension being kept up for some 

 time after the operation. 



f 



MUSCLES AND FASCIJB OF THE LEG. 



Dissection (fig. 186). The knee should be bent, a block placed beneath it, and the foot kept 

 m an extended position ; an incision should then be made through the integument in the middle 

 line of the leg to the ankle, and continued along the dorsum of the foot to the toes. A second 

 incision should be made transversely across the ankle, and a third in the same direction across 

 the bases of the toes : the flaps of integument included between these incisions should be 

 removed, and the deep fascia of the leg examined. 



The fascia of the leg forms a complete investment to the whole of this region 

 of the limb, excepting to the inner surface of the tibia, to which it is unattached. 

 It is continuous above with the fascia lata, receiving an expansion from the 

 tendon of the Biceps on the outer side, and from the tendons of the Sartorius, 

 Gracilis, and Semi-tendinosus on the inner side; in front it blends with the 

 periosteum covering the tibia and fibula ; below, it is continuous with the annular 

 ligaments of the ankle. It is thick and dense in the upper and anterior part of 



