486 MYOLOGY 





the anterior tibial vessels pass forward to the front of the leg. It arises from the 

 whole of the posterior surface of the interosseous membrane, excepting its lowest 

 part; from the lateral portion of the posterior surface of the body of the tibia, 

 between the commencement of the popliteal line above and the junction of the 

 middle and lower thirds of the body below; and from the upper two-thirds of the 

 medial surface of the fibula; some fibers also arise from the deep transverse fascia, 

 and from the intermuscular septa separating it from the adjacent muscles. In 

 the lower fourth of the leg its tendon passes in front of that of the Flexor digitorum 

 longus and lies with it in a groove behind the medial malleolus, but enclosed in a 

 separate sheath; it next passes under the laciniate and over the deltoid ligament 

 into the foot, and then beneath the plantar calcaneonavicular ligament. The 

 tendon contains a sesamoid fibrocartilage, as it runs under the plantar calcaneo- 

 navicular ligament. It is inserted into the tuberosity of the navicular bone, and 

 gives off fibrous expansions, one of which passes backward to the sustentaculum tali 

 of the calcaneus, others forward and lateralward to the three cuneiforms, the 

 cuboid, and the bases of the second, third, and fourth metatarsal bones. 



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

 the Flexor digitorum longus and Tibialis posterior by the fifth lumbar and first sacral, and the 

 Flexor hallucis longus by the fifth lumbar and the first and second sacral nerves, through the 

 tibial nerve. 



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 beginning of the act of bending 

 the knee, inasmuch as it produces the slight inward rotation of the tibia which is essential in the 

 early stage of this movement. The Tibialis posterior is a direct extensor of the foot at the ankle- 

 joint; acting in conjunction with the Tibialis anterior, it turns the sole of the foot upward and 

 medialward, i. e., inverts the foot, antagonizing the Peronsei, which turn it upward and lateral- 

 ward (evert it). In the sole of the foot the tendon of the Tibialis posterior lies directly below the 

 plantar calcaneonavicular ligament, and is therefore an important factor in maintaining the 

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

 the phalanges, and, continuing their action, extend the foot upon the leg; they assist the Gastroc- 

 nemius and Soleus in extending the foot, as in the act of walking, or in standing on tiptoe. In 

 consequence of the oblique direction of its tendons the Flexor digitorum longus would draw the 

 toes medialward, were it not for the Quadratus plantse, which is inserted into the lateral side 

 of the tendon, and draws it to the middle line of the foot. Taking their fixed point from the 

 foot, these muscles serve to maintain the upright posture by steadying the tibia and fibula 

 perpendicularly upon the talus. 



3. The Lateral Crural Muscles (Fig. 439). 

 Peronseus longus. Peronaeus brevis. 



The Peronaeus longus is situated at the upper part of the lateral side of the 

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

 upper two-thirds of the lateral surface of the body of the fibula, from the deep 

 surface of the fascia, and from the intermuscular septa between it and the muscles 

 on the front and back of the leg; occasionally also by a few fibers from the lateral 

 condyle of the tibia. Between its attachments to the head and to the body of the 

 fibula there is a gap through which the common peroneal nerve passes to the front 

 of the leg. It ends in a long tendon, which runs behind the lateral malleolus, in 

 a groove common to it and the tendon of the Peronseus brevis, behind which it 

 lies; the groove is converted into a canal by the superior peroneal retinaculum, and 

 the tendons in it are contained in a common mucous sheath. The tendon then 

 extends obliquely forward across the lateral side of the calcaneus, below the troch- 

 lear process, and the tendon of the Peronseus brevis, and under cover of the inferior 

 peroneal retinaculum. It crosses the lateral side of the cuboid, and then runs on the 

 under surface of that bone in a groove which is converted into a canal by the long 

 plantar ligament; the tendon then crosses the sole of the foot obliquely, and is 

 inserted into the lateral side of the base of the first metatarsal bone and the lateral 



