THE OUTER OR FIBULAR REGION. 527 



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

 they assume in the stooping posture. 



Outer or Fibular Region. 

 Peroneus longus. Peroneus brevis. 



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

 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. 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 forward, 

 across the outer side of the os calcis, 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 and the internal cuneiform 

 bone. 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 fibre-cartilage, 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, 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 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 intennuscular 

 septa separating it from the adjacent muscles on the front and back part of the 

 leg. The fibres pass vertically downward, and terminate 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, and 

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

 toe. on its outer side. 



Relations. By its superficial surface, with the Peroneus longus and the fascia 

 of the leg and foot ; by its deep surface, with the fibula and outer side of the os 

 calcis. 



Nerves. The Peroneus longus and brevis are supplied by the musculo-cuta- 

 neous branch of the external popliteal nerve. 



Actions. The Peroneus longus and brevis extend the foot upon the leg in 

 conjunction with the Tibialis posticus. antagonizing the Tibialis anticus and 

 Peroneus tertius. which are flexors of the foot. The Peroneus longus also everts 

 the sole of the foot ; hence the extreme eversion occasionally observed in fractui'e 

 of the lower end of the fibula, where that bone offers no resistance to the action 

 of this muscle. Taking their fixed point below, the Peronei serve to steady the 

 leg upon the foot. This is especially the case in standing upon one leg, when the 



