440 THE MUSCLES AND FASCIA. 



commencement of the oblique line above, and the junction of the middle and lower 

 third of the shaft below ; and from the upper two-thirds of the internal surface of 

 the fibula ; some fibres also arise from the deep transverse fascia and from the 

 intermuscular septa, separating it from the adjacent muscles on each side. This 

 muscle, in the lower fourth of the leg, passes in front of the Flexor longus 

 digitorum, and terminates in a tendon which passes through a groove behind 

 the inner malleolus with the tendon of that muscle, but enclosed in a separate 

 sheath ; it then passes through another sheath, over the internal lateral liga- 

 ment into the foot, and then beneath the inferior calcaneo-navicular ligament, 

 and is inserted into the tuberosity of the navicular and internal cuneiform bones. 

 The tendon of this muscle contains a sesamoid fibro-cartilage as it passes over the 

 navicular bone, and gives off fibrous expansions, one of which passes backward to 

 the sustentaculum tali of the os calcis, others outward to the middle and external 

 cuneiform and cuboid, and some forward to the bases of the second, third, and 

 fourth metatarsal bones (Fig. 263). 



Relations. By its superficial surface, with the Soleus, from which it is 

 separated by the deep transverse fascia, the Flexor longus digitorum, the posterior 

 tibial vessels and nerve, and the peroneal vessels ; by its deep surface, with the 

 interosseous ligament, the tibia, fibula, and ankle-joint. 



Nerves. The Popliteus is supplied by the fourth and fifth lumbar and first sacral 

 nerves, through the internal popliteal ; the Flexor longus digitorum and Tibialis 

 posticus by the fifth lumbar and first sacral ; and the Flexor longus hallucis by the 

 fifth lumbar and first and second sacral nerves through the posterior tibial. 



Actions. The Popliteus assists in flexing the leg upon the thigh ; when the leg 

 is flexed, it will rotate the tibia inward. It is especially called into action at the 

 commencement of the act of bending the knee, inasmuch as it produces a slight 

 inward rotation of the tibia, which is essential in the early stage of this movement. 

 The Tibialis posticus is a direct extensor of the foot at the ankle-joint; acting in 

 conjunction with the Tibialis anticus, it turns the sole of the foot inward (i. e., 

 inverts the foot), antagonizing the Peronei, which turn it outward (evert it). In 

 the sole of the foot the tendon of the Tibialis posticus lies directly below the inferior 

 calcaneo-scaphoid ligament, and is therefore an important factor in maintaining the 

 arch of the foot. The Flexor longus digitorum and Flexor longus hallucis are the 

 direct flexors of the phalanges, and, continuing their action, extend the foot upon 

 the leg ; they assist the Gastrocnemius and Soleus in extending the foot, as in the 

 act of walking or in standing on tiptoe. 



In consequence of the oblique direction of the tendon of the long flexor the 

 toes would be drawn inward were it not for the Flexor accessorius muscle, which 

 is inserted into the outer side of its tendon and draws it to the middle line of the 

 foot during its action. Taking their fixed point from the foot, these muscles serve 

 to maintain the upright posture by steadying the tibia and fibula perpendicularly 

 upon the ankle-joint. They also serve to raise these bones from the oblique posi- 

 tion they assume in the stooping posture. 



7. Fibular Region. 



Peroneus longus. Peroneus brevis. 



Dissection. The muscles are readily exposed by removing the fascia covering their surface, 

 from below upward, in the line of direction of their fibres. 



The Peroneus longus is situated at the upper part of the outer side of the leg, 

 and is the more superficial of the two muscles. It arises from the head and upper 

 two-thirds of the outer surface of the shaft of the fibula, from the deep surface of 

 the fascia, and from the intermuscular septa between it and the muscles on the 

 front, and those on the back of the leg, occasionally also by a few fibres from the 

 outer tuberosity of the tibia. Between its attachment to the head and to the 

 shaft of the fibula there is a small interval of bone from which no muscular fibres 

 arise ; through this gap the external popliteal nerve passes beneath the muscle. 



