536 THE MUSCLES AND FASCIAE 



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. 



7. The Fibular Region (Fig. 383). 

 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 (m. peronaeus 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 muscle fibres arise; through this gap the external popliteal nerve passes 

 beneath the muscle. The muscle terminates in a long tendon, which passes be- 

 hind the outer malleolus, in a groove common to it and the tendon of the Peroneus 

 brevis, behind which it lies, the groove being converted into a canal by a fibrous 

 band, and the tendons being invested by a common synovial membrane; it is 

 then reflected obliquely forward across the outer side of the os calcis, below its 

 peroneal tubercle, being contained in a separate fibrous sheath, lined by a pro- 

 longation of the synovial membrane 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 calcaneocuboid 

 ligament, and is lined by a synovial membrane; the tendon then crosses the sole 

 of the foot obliquely, and is inserted into the outer side of the base of the meta- 

 tarsal bone of the great toe and the internal cuneiform bone (Figs. 399 and*flOO). 

 Occasionally it sends a slip to the base of the second metatarsal bone. 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 fibrocartilage, or sometimes a 

 bone, is usually developed in its substance. 



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

 with the fibula, external popliteal nerve, the Peroneus brevis, os calcis, 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 intermuscular septum, which separates it from 

 the Soleus above and the Flexor longus hallucis below. 



The Peroneus brevis (m. peronaeus brevis) lies beneath the Peroneus longus, 

 and is shorter and smaller than it. It arises from the lower two-thirds of the 

 external surface of the shaft of the fibula, internal to the Peroneus longus, and 

 from the intermuscular septa separating it from the adjacent muscles on the 

 front and back part of the leg. The fibres pass vertically downward, and termi- 

 nate in a tendon which runs in front of that of the preceding muscle through the 

 same groove, behind the external malleolus, being contained in the same fibrous 

 sheath and lubricated by the same synovial membrane. It then passes through 

 a separate sheath on the outer side of the os calcis, above that for the tendon of 

 the Peroneus longus, the two tendons being here separated by the peroneal tubercle, 

 and is finally inserted into the tuberosity at the base of the metatarsal bone of 

 the little toe, on its outer side. 



