438 THE MUSCLES AND FASCIAE. 



and the Plantaris by the fourth and fifth lumbar and first sacral nerves through the 

 internal popliteal. The Soleus is supplied by the fifth lumbar and first and second 

 sacral nerves through the internal popliteal and posterior tibial. 



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 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 forward. In standing, the Soleus, 

 taking its fixed point from below, steadies the leg upon the foot, and prevents the 

 body from falling forward, to which there is a constant tendency from the superin- 

 cumbent 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 is continued over the os cal- 

 cis to be inserted into the plantar fascia. In man it is an accessory to the Gastroc- 

 nemius, extending the ankle if the foot is free, or bending the knee if the foot is 

 fixed. Possibly, acting from below, by its attachment to the posterior ligament 

 of the knee-joint, it may pull that ligament backward during flexion, and so pro- 

 tect it from being compressed between the two articular surfaces. 



Deep Layer (Fig. 260). 



Popliteus. Flexor longus digitorum. 



Flexor longus hallucis. Tibialis posticus. 



Dissection. Detach the Soleus from its attachment to the fibula and tibia, and turn it 

 downward, when the deep layer of muscles is exposed, covered by the deep transverse fascia of 

 the leg. 



The Deep Transverse Fascia of the leg is a transversely placed, intermuscular 

 septum, between the superficial and deep muscles in the posterior tibio-fibular region. 

 On either side it is connected to the margins of the tibia and fibula. Above, where 

 it covers the Popliteus, it is thick and dense, and receives an expansion from the 

 tendon of the Semimembranosus ; it is thinner in the middle of the leg, but below, 

 where it covers the tendons passing behind the malleoli, it is thickened and con- 

 tinuous with the internal annular ligament. 



This fascia should now be removed, commencing from below opposite the tendons, and 

 detaching it from the muscles in the direction of their fibres. 



The Popliteus is a thin, flat, triangular muscle, which forms part of~the floor of 

 the popliteal space. It arises by a strong tendon, about an inch in length, from a 

 deep depression on the outer side of the external condyle of the femur, and from 

 the posterior ligament of the knee-joint, and is inserted into the inner two-thirds of 

 the triangular surface above the oblique line on the posterior surface of the shaft of 

 the tibia, and into the tendinous expansion covering the surface of the muscle. 

 The tendon of the muscle is covered by that of the Biceps and by the external lat- 

 eral ligament of the knee-joint ; it grooves the posterior border of the external semi- 

 lunar fibro-cartilage, and is invested by the sy no vial membrane of the knee-joint. 



Relations. By its superficial surface, with the fascia covering it, which separates 

 it from the Gastrocnemius, Plantaris. popliteal vessels, and internal popliteal nerve ; 

 by its deep surface, with the knee-joint and back of the tibia. 



The Flexor longus hallucis is situated on the fibular side of the leg, and is the 

 most superficial and largest of the three next muscles. It arises from the lower 

 two-thirds of the posterior surface of the shaft of the fibula, with the exception of 

 an inch at its lowest . part ; from the lower part of the interosseous membrane ; 

 from an intermuscular septum between it and the Peronei, externally ; and from 

 the fascia covering the Tibialis posticus internally. The fibres pass obliquely 

 downward and backward, and terminate in a tendon which occupies nearly the 

 whole length of the posterior surface of the muscle. This tendon occupies a groove 

 on the posterior surface of the lower end of the tibia ; it then lies in a second groove 



