FIBULAR REGIOX. 347 



another sheath, over the internal lateral ligament, and beneath the calcaneo- 

 scaphoid articulation, and is inserted into the tuberosity of the scaphoid, and 

 internal cuneiform bones. The tendon of this muscle contains a sesamoid bone, 

 near its insertion, and gives off fibrous expansions, one of which passes back- 

 wards to the os calcis, some outwards to the middle and external cuneiform, and 

 others forwards to the bases of the third and fourth metatarsal bones. 



Relations. By its superficial surface, with the Soleus and Flexor longus 

 digitorum, the posterior tibial vessels and nerve, and the peroneal vessels, from 

 which it is separated by the deep fascia. By its deep surface, with the interosseous 

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



Nerves. The Popliteus is supplied by the internal popliteal nerve, the remaining 

 muscles of this group by the posterior tibial nerve. 



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

 is flexed, it may rotate the tibia inwards. The Tibialis posticus is a direct extensor 

 of the tarsus upon the leg; acting in conjunction with the Tibialis anticus, it 

 turns the sole of the foot inwards, antagonizing the Peroneus longus which 

 turns it outwards. The Flexor longus digitorum and Flexor longus pollicis 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 extensor, the toes would be drawn inwards, 

 were it not for the Flexor accessorius muscle, which is inserted into the outer side 

 of that 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 position they assume in the 

 stooping posture. 



FIBULAE EEGION. 



Peroneus Longus. Peroneus Brevis. 



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

 from below upwards, 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 

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

 and those on the back of the leg. It terminates in a long tendon, which passes 

 behind the outer malleolus, in a groove, common to it and the Peroneus brevis, 

 the groove being converted into a canal by a fibrous band, and the tendons 

 invested by a common synovial membrane ; it is then reflected, obliquely forwards, 

 across the outer side of the os calcis, being contained in a separate fibrous sheath, 

 lined by a prolongation of the synovial membrane, from the groove behind 

 the malleolus. Having reached the outer side of the cuboid bone, it runs, in a 

 groove, on its under surface, which is converted into a canal by the long calcaneo- 

 cuboid ligament, lined by a synovial membrane, and crossing, obliquely, the sole 

 of the foot, is inserted into the outer side of the base of the metatarsal bone of 

 the great toe. The tendon of the muscle has a double reflection, first, behind the 

 external malleolus, secondly, on the outer side of the cuboid bone ; in both of 

 these situations, the tendon is thickened, and, in the latter, a sesamoid bone is 

 usually developed in its substance. 



Relations. By its superficial surface, with the fascia and integument. By its 

 deep surface, with the fibula, the Peroneus brevis, os calcis, and cuboid bone. 

 By its anterior border, an intermuscular septum intervenes between it and the 

 Extensor longus digitorum. By its posterior border, an intermuscular septum 

 separates it from the Soleus above, and the Flexor longus pollicis below. 



