530 THE MUSCLES AND FASCIA 



cular septum between it and the Peroneus brevis. The tendon, after passing 

 through the same canal in the annular ligament as the Extensor longus digito- 

 rum, is inserted into the dorsal surface of the base of the metatarsal bone of the 

 little toe. This muscle is sometimes wanting. 



Nerves. These muscles are supplied by the fourth and fifth lumbar and first sacral nerves 

 through the anterior tibial nerve. 



Actions. The Tibialis anticus and Peroneus tertius are the direct Flexors of the foot at the 

 ankle-joint; the former muscle, when acting in conjunction with the Tibialis posticus, raises 

 the inner border of the foot (i. e., inverts the foot) ; and the latter, acting with the Peroneus 

 brevis and longus, draws the outer border of the foot upward, and the sole outward (i. e., everts 

 the foot). The Extensor longus digitorum and Extensor proprius hallucis extend the phalanges 

 of the toes, and, continuing their action, flex the foot upon the leg. Taking their fixed point from 

 below, in the erect posture, all these muscles serve to fix the bones of the leg in the perpendicular 

 position, and give increased strength to the ankle-joint. 



6. The Posterior Tibiofibular Region (Figs. 391, 396). 



Dissection (Fig. 386). Make a vertical incision along the middle line of the back of the leg, 

 from the lower part of the popliteal space to the heel, connecting it below by a transverse incision 

 extending between the two malleoli; the flaps of integument being removed, the fascia and 

 muscles should be examined. 



The muscles in this region of the leg are subdivided into two layers superficial 

 and deep. The superficial layer constitutes a powerful muscular mass, forming 

 the calf of the leg. Their large size is one of the most characteristic features of 

 the muscular apparatus in man, and bears a direct connection with his ordinary 

 attitude and mode of progression. 



The Superficial Layer. 

 Gastrocnemius. Soleus. Plantaris. 



The Gastrocnemius (m. gastrocnemius) is the most superficial muscle, and 

 forms the greater part of the calf. It arises by two heads, which are connected 

 to the condyles of the femur by two strong flat tendons. The inner and larger 

 head (caput mediale) arises from a depression at the upper and back part of the 

 inner condyle and from the adjacent part of the femur. The outer head (caput 

 laterale) arises from an impression on the outer side of the external condyle and 

 from the posterior surface of the femur immediately above the condyle. Both 

 heads, also, arise by a few tendinous and fleshy fibres from the ridges which are 

 continued upward from the condyles to the linea aspera. Each tendon spreads 

 out into an aponeurosis, which covers the posterior surface of that portion of the 

 muscle to which it belongs; the muscle fibres of the inner head form a thicker mass 

 and extend lower than those of the outer. From the anterior surface of these 

 tendinous expansions muscle fibres are given off. The fibres in the median line, 

 which correspond to the accessory portions of the muscle derived from the bifur- 

 cations of the linea aspera, unite at an angle upon a median tendinous raphe' 

 below; the remaining fibres converge to an aponeurosis which covers the anterior 

 surface of the muscle, and this, gradually contracting, unites with the tendon 

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



Relations. -By its superficial surface, with the fascia of the leg, which separates it from the 

 external saphenous vein and nerve; by its deep surface, with the 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 



