FIBULAR REGION. 425 



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 interos- 

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



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

 maining 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 will 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, arid 

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

 fascia, and from the iutermuscular 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 ten- 

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

 forwards, across the outer side of the os caicis, being contained in a separate 

 fibrous sheath, lined by a prolongation of the synovial membrane from that 

 which lines the groove behind the malleolus. Having reached the outer side 

 of the cuboid bone, it runs in a groove on the under surface of that bone, which 

 is converted into a canal by the long calcaneo-cuboid ligament, and is lined by 

 a synovial membrane : the tendon then crosses, obliquely, the sole of the foot, 

 and is inserted into the outer side of the base of the metatarsal bone of the 

 great toe. The tendon changes its direction at two points, 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 caicis and cuboid bone; 

 by its anterior border, with an intermuscular septum, which intervenes between 

 it and the Extensor Longus Digitorum; by its posterior border, with an intermus- 

 cular septum, which separates it from the Soleus above, and the Flexor Longus 

 Pollicis below. 



The Peroneus Brevis lies beneath the Peroneus Longus, and is shorter and 

 smaller than it. It arises from the middle third of the external surface of the 

 shaft of the fibula, internal to the Peroneus Longus ; from the anterior and 

 posterior borders of the bone ; and from the intermuscular septa separating it 

 from the adjacent muscles on the front and back part of the leg. The fibres 



