344 MUSCLES AND FASCIA. 



posterior ligament of the knee-joint, -the Popliteus, Soleus, Plantaris, popliteal 

 vessels, and internal popliteal nerve. The tendon of the inner head corresponds 

 with the back part of the inner condyle, from which it is separated by a synovial 

 bursa, which, in some cases, communicates with the cavity of the knee-joint. The 

 tendon of the outer head contains a sesamoid fibre-cartilage, rarely osseous, where 

 it plays over the corresponding outer condyle ; and one is occasionally found in 

 the tendon of the inner head. 



The Gastrocnemius should be divided across, just below its origin, and turned downwards, in 

 order to expose the next muscles. 



The Soletis is a broad flat muscle, situated immediately beneath the preceding. 

 It has received its name from the fancied resemblance it bears to a sole-fish. It 

 arises by tendinous fibres from the back part of the head, and from the upper 

 half of the posterior surface of the shaft of the fibula, from the oblique line of 

 the tibia, and from the middle third of its internal border ; some fibres also arise 

 from a tendinous arch placed between the tibial and fibular origins of the muscle, 

 and beneath which the posterior tibial vessels and nerve pass into the leg. The 

 fibres pass backwards to an aponeurosis which covers the posterior surface of the 

 muscle, and this, gradually becoming thicker and narrower, joins with the tendon 

 of the Gastrocnemius, and forms with it the tendo Achillis. 



Relations. By its superficial surface, with the Gastrocnemius and Plantaris. By 

 its deep surface, with the Flexor longus digitorum, Flexor longus pollicis, Tibialis 

 posticus, and posterior tibial vessels and nerve, from which it is separated by the 

 transverse intermuscular septum. 



The tendo Achillis, the common tendon of the Gastrocnemius and Soleus, is 

 the thickest and strongest tendon in the body. It is about six inches in length, 

 and formed by the junction of the aponeuroses of the two preceding muscles. It 

 commences about the middle of the leg, but receives fleshy fibres on its anterior 

 surface, nearly to its lower end. Gradually becoming contracted below, it is 

 inserted into the lower part of the posterior tuberosity of the os calcis, a synovial 

 bursa being interposed between the tendon and the upper part of the tuberosity. 

 The tendon is covered by the fascia and the integument, and is separated from the 

 deep muscles and vessels, by a considerable interval filled up with areolar and 

 adipose tissue. Along its outer side, but superficial to it, is the external saphe- 

 nous vein. 



The Plantaris is an extremely diminutive muscle, placed between the Gastroc- 

 nemius and Soleus, and remarkable for its long and delicate tendon. It arises 

 from the lower part of the outer bifurcation of the linea aspera, and from the 

 posterior ligament 'of "the knee-joint. It forms a small fusiform belly, about two 

 inches in length, terminating in a long slender tendon, which crosses obliquely 

 between the two muscles of the calf, and, running along the inner border of the 

 tendo Achillis, is inserted with it into the posterior part of the os calcis. This 

 muscle is occasionally double, and is sometimes wanting. At times, its tendon 

 is lost in the internal annular ligament, or in the fascia of the leg. 



Nerves. These muscles are supplied by the internal popliteal nerve. 



Actions. The muscles of the calf possess considerable power, and are con- 

 stantly called into use in standing, walking, dancing, and leaping ; hence the large 

 size they usually present. In walking, these muscles draw powerfully upon the 

 os calcis, raising the heel, and, with it, the entire body, from the ground ; the body 

 being thus supported on the raised foot, the opposite limb can be carried forwards. 

 In standing, the Soleus, taking its fixed point from below, steadies the leg upon 

 the foot, and prevents the body from falling forwards, to which there is a constant 

 tendency from the superincumbent weight. The Gastrocnemius, acting from 

 below, serves to flex the femur upon the tibia, assisted by the Popliteus. The 

 Plantaris is the rudiment of a large muscle which exists in some of the lower 

 animals, and serves as a tensor of the plantar fascia. 



