292 MUSCLES AND FASCIAE OF THE LOWER LIMB. 



The gastrocnemius muscle acts both as a flexor of the knee and as an extensor of 

 the foot. When the anterior muscles of the leg fix the ankle-joint, it is fitted to act 

 as a flexor of the knee ; when the knee is fixed either by being placed in complete 

 extension or by the sustained action of the extensor muscles, the gastrocnemius acts 

 entirely on the foot, and combines with the soleus in extending the ankle and astragalo- 

 calcaneal joints. By the complete contraction of these muscles the heel is lifted from 

 the ground and the body is raised on the toes. In leaping, as the limb is suddenly 

 straightened by extension both at the knee and ankle joints, the gastrocnemius acts in 

 the most advantageous manner possible on the foot, seeing that by the movement of 

 the knee its fibres are kept stretched. 



The tibialis anticus muscle flexes the foot upon the leg and raises its inner side : 

 the peroneus tertius flexes the foot and raises its outer side : the tibialis posticus 

 extends the foot and gives it an inward direction : the peroneus longus and brevis 

 extend the foot and give it an outward direction. The peroneus longus, in crossing 

 the foot inferiorly, strengthens the transverse arch formed by the metatarsal bones and 

 anterior range of tarsal bones ; especially when that arch is pressed upon by the 

 weight of the body falling on the balls of the toes, as in stooping with bended knees. 



The/exor and extensor muscles of the toes, including the lumbricales, act like the 

 corresponding muscles in the hand. The direction of the flexor longus digitorum is, 

 however, modified by the flexor accessorius, so as to bring its line of action into the 

 direction of the middle of the foot and of the short flexor. The flexor accessorius and 

 tendon of the foot and of the long flexor likewise assist the short flexor and the plantar 

 aponeurosis in maintaining the arch of the foot. 



FASCIAE OF THE LOWER LIMB. 



The superficial fascia of the lower limb is similar to that of other parts of 

 the body. The subcutaneous layer is continuous with that of the lower 

 part of the abdomen. The disposition of the deeper and more membranous 

 part on the front of the thigh deserves attention in respect that it is so firmly 

 attached to Poupart's ligament as to prevent the passage of fluids under it, 

 from the thigh to the abdomen. 



The aponeurosis of the lower limb, or fascia lata, is similar to the aponeu- 

 rosis of the upper limb, but in some parts much stronger. 



In the gluteal region it is attached to the crest of the ilium, and descends 

 as a strong membrane on the surface of the gluteus medius, as far as the 

 upper margin of the gluteus maximus muscle ; it there divides into two 

 layers, one superficial to the gluteus maximus, a continuous sheet, attached 

 at its inner end to the sacrum, the other on the deep surface of that muscle. 

 These two layers incase the muscle, and again unite at its inferior margin. 



On the thigh the fascia lata forms a continuous sheath, varying in thick- 

 ness in different parts. It is strongest on the outer aspect of the limb, 

 where its dense and glistening parallel fibres give it much the appearance of 

 a tendinous aponeurosis, and where it serves the purpose of a tendon to the 

 tensor vaginse femori?, and to a large part of the gluteus maximus. It is 

 thinnest in the upper and inner part of the thigh, where it covers the 

 adductor muscles. Near the knee it is considerably strengthened by ten- 

 dinous expansions given off from the lower termination of the extensor and 

 flexor muscles of the knee-joint. 



In front of the thigh, a little below and external to the inner end of 

 Poupart's ligament, is placed the saphenous opening, an aperture in the 

 fascia lata through which the internal saphenous vein passes to join the 

 femoral vein, and which receives special attention from its being the place 

 of exit of femoral hernia. The outer part of this opening extends to the 

 femoral artery, and is bounded externally by a crcscentic margin, the fal- 



