368 THE MUSCLES 



nrrve to the vastus internus beiiiir a large and conspicuous branch wliich lies close 

 to the outer side of the superticial femoral artery in the upper part of Hunter's 

 canal. 



Action. — The vastiis externus, crureus, and vastus internus, together with the 

 rectus fenioris, extend powerfully the knee. Their intermediate insertion into 

 the sesamoid bone formed by the patella serves to lift from the line of the tibia the 

 ligamentum patelhe, which may be looked upon as the lower part of their common 

 tendon. The enormous power of the whole of this combination of muscles is 

 necessitated partly by the fact that the whole of the weight of the body has to be 

 raised by it, and partly by the great mechanical disadvantage which results from 

 the short arm of the lever upon which the tendon acts, and the obliquity of its 

 insertion. 



On account of the direction of the femur, which is downwards and inwards, the 

 tendency of the quadriceps is to draw the patella outwards at the same time as up- 

 wards. This is in some degree counteracted by the position and direction of the 

 vastus internus. The great mass of the fibres of this part of the quadriceps arises in 

 the lower part of the thigh, and is directed so transversely outwards towards the 

 inner border of the patella, that when it contracts it tends to draw the patella 

 inwards as well as upwards, and so the resviltant of the various divisions of the 

 (juadriceps when contracting simultaneously is to draw the patella more directly 

 upwards. If it were not for this arrangement, the contraction of the quadriceps 

 would have a strong tendency to produce outward dislocation of the knee-cap. 



Relations of vastus externus, crureus, and vastus internus. — In front lie 

 the fascia lata, tensor vaginse femoris, rectus femoris, and sartorius. To the inner 

 side lie the femoral vessels and anterior crural nerve. On the outer side are the 

 gluteus minimus and maximus. Behind are the biceps on the outer side of the 

 femur, and the adductor longus and magnus on the inner side. 



Variations. — These are few in number. An accessory head to the rectus from the anterior 

 superior ^yime of the iUum has been described, and occasionally the outer head is absent. 



THE DEEP FASCIA OF THE LEG AND ANNULAR LIGAMENTS 



The deep fascia of the leg is continuous above with the fascia lata of the thigh 

 and receives imj^ortant additions from the tendons of the quadriceps, biceps, 

 sartorius, gracilis, and semi-tendinosus. It is also attached to the lower j)art of the 

 outer and inner tuberosities of the tibia and to the head of the fibula. At the liack 

 of the knee it is strengthened by transverse fibres which serve to bind together the 

 muscles which form the boundaries of the popliteal space; the external saphenous 

 vein also perforates it about the centre of the space. It is very thick and strong 

 at the upper and outer part of the front of the leg; but behind, where it covers the 

 muscles of the calf, the fascia becomes much thinner. The internal surface of the 

 tibia is not covered by this fascia, which blends with the periosteum covering its 

 anterior and inner borders throughout their whole length. It is also attached to the 

 borders of the fibula by two strong intermuscular septa which form the anterior and 

 posterior walls of a compartment containing the long and short peronei. In the 

 lower third of the leg it is attached to the borders of the subcutaneous surface of 

 the fibula. In the neiglibourhood of the ankle the deep fascia is thickened by the 

 addition of numerous transverse fibres, and forms the annular ligaments. 



The anterior annular ligament (fig. 298) consists of two parts, an upper and 

 a loicer. The upjicr purl is a strong band of transverse fibres just above the ankle- 

 joint, which extends from the anterior border of the tibia to the anterior border of 

 the subcutaneous surface of the fibula. Behind it there is a separate synovial 

 sheath for the tendon of the tibialis anticus. The Inwer part of the anterior annular 

 ligament arises from the u])])er surface and outer border of the great process 

 of the calcaneuni in two bands, a su])erficial and a deep, which, passing trans- 

 versely inwards, unite after a course of about an inch (2-5 cm.), and thus form 

 a loop in which are contained the tendons of the extensor longus digitorum and the 

 peroneus tertius, together with part of the origin of the extensor brevis digitorum. 



