

THE POSTERIOR CRURAL MUSCLES 483 



Variations. Absence of the outer head or of the entire muscle. Extra slips from the popliteal 

 surface of the femur. 



The Soleus is a broad flat muscle situated immediately in front of the Gastroc- 

 nemius. It arises by tendinous fibers from the back of the head of the fibula, 

 and from the upper third of the posterior surface of the body of the bone ; from the 

 popliteal line, and the middle third of the medial border of the tibia; some fibers 

 also arise from a tendinous arch placed between the tibial and fibular origins 

 of the muscle, in front of which the popliteal vessels and tibial nerve run. The 

 fibers end in an aponeurosis .which covers the posterior surface of the muscle, and, 

 gradually becoming thicker and narrower, joins with the tendon of the Gastroc- 

 nemius, and forms with it the tendo calcaneus. 



Variations. Accessory head to its lower and inner part usually ending in the tendocalcaneus, or 

 the calcaneus, or the laciniate ligament. 



The Gastrocnemius and Soleus together form a muscular mass which is occa- 

 sionally described as the Triceps surse ; its tendon of insertion is the tendo calcaneus. 



Tendo Calcaneus (tendo Achillis) . The tendo calcaneus, the common tendon of the 

 Gastrocnemius and Soleus, is the thickest and strongest in the body. It is about 

 15 cm. long, and begins near the middle of the leg, but receives fleshy fibers on its 

 anterior surface, almost to its lower end. Gradually becoming contracted below, 

 it is inserted into the middle part of the posterior surface of the calcaneus, a bursa 

 being interposed between the tendon and the upper part of this surface. The ten- 

 don spreads out somewhat at its lower end, so that its narrowest part is about 

 4 cm. above its insertion. It 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 lateral side, but superficial to it, is the 

 small saphenous vein. 



The Plantaris is placed between the Gastrocnemius and Soleus. It arises from 

 the lower part of the lateral prolongation of the linea aspera, and from the oblique 

 popliteal ligament of the knee-joint. It forms a small fusiform belly, from 7 to 

 10 cm. long, ending in a long slender tendon which crosses obliquely between the 

 two muscles of the calf, and runs along the medial border of the tendo calcaneus, 

 to be inserted with it into the posterior part of the calcaneus. This muscle is some- 

 times double, and at other times wanting. Occasionally, its tendon is lost in the 

 laciniate ligament, or in the fascia of the leg. 



Nerves. The Gastrocnemius and Soleus are supplied by the first and second sacral nerves, 

 and the Plantaris by the fourth and fifth lumbar and first sacral nerves, through the tibial nerve. 



Actions. The muscles of the calf are the chief extensors of the foot at the ankle-joint. They 

 possess considerable power, and are constantly called into use in standing, walking, dancing, 

 and leaping; hence the large size they usually present. In walking, these muscles raise the heel 

 from the ground; the body being thus supported on the raised foot, the opposite limb can be 

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

 the foot and prevents the body from falling forward. 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 in some of the lower animals is continued over the calcaneus to be inserted 

 into the plantar aponeurosis. In man it is an accessory to the Gastrocnemius, extending the 

 ankle if the foot be free, or bending the knee if the foot be fixed. 





The Deep Group (Fig. 439). 



Popliteus. Flexor digitorum longus. 



Flexor hallucis longus. Tibialis posterior. 



Deep Transverse Fascia. The deep transverse fascia of the leg is a transversely 

 placed, intermuscular septum, between the superficial and deep muscles of the 

 back of the leg. At the sides it is connected to the margins of the tibia and 



