THE LOWER LIMB 5^1 



and inwards. In that part of the tendon which turns round the 

 outer border of the cuboid a sesamoid fibro-cartilage is found. 



Peroneus Brevis — Origin. — (i) The lower two-thirds of the ex- 

 ternal surface of the shaft of the fibula, except the last 2 inches ; 



(2) the antero-extemal and postero-external intermuscular septa ; 

 and (3) the deep fascia. 



Insertion. — ^The tuberosity on the outer side of the base of the 

 fifth metatarsal bone. From the tendon of insertion a slip is often 

 given to the long extensor tendon of the httle toe. 



Nerve-supply. — ^The musculo-cutaneous nerve. 



Action. — (i) To extend the foot upon the leg, but in a feeble 

 manner ; (2) to abduct or turn out the fore part of the foot ; and 



(3) to raise directly the outer border of the foot, thus producing 

 eversion of the sole. 



The middle third of the external surface of the fibula is occupied 

 by both peroneus longus and peroneus brevis, the former arising 

 from the posterior half, and the latter from the anterior half, so 

 that the two muscles overlap. The tendon of the peroneus brevis 

 passes through the groove behind the external malleolus with the 

 tendon of the peroneus longus, which is directly behind it. Both 

 tendons lie beneath the external annular ligament, where they have 

 one synovial sheath in common. After leaving the malleolar 

 groove the tendon of the peroneus brevis passes forwards on the 

 outer surface of the os calcis, where it occupies the groove above 

 the peroneal spine or ridge. In this part of its course the tendon 

 is surrounded by a fibrous sheath, which is derived from the lower 

 border of the external annular ligament, and it is here invested by 

 a special synovial sheath, which is a prolongation of that beneath 

 the external annular ligament. After leaving the outer surface 

 of the OS calcis the tendon passes over the cuboid bone, and so reaches 

 its insertion. 



On the outer surface of the os calcis the two peroneal tendons are 

 completely separated from each other, that of the brevis being 

 above that of the longus. The separation is effected partly by a 

 strong fibrous septum, and partly by the peroneal spine or ridge. 

 The peroneus longus and peroneus brevis are contained in a fibro- 

 osseous canal formed by the deep fascia, the intermuscular septum 

 on each side, and the external surface of the shaft of the fibula. 



Posterior Aspect of the Leg. 



Superficial Structures. — The following superficial structures are 

 met with in this region : the external or short saphenous vein, 

 the cutaneous sural branches of the pophteal artery, the terminal 

 part of the small sciatic ner\'e, the ramus communicans tibialis 

 nerve, the ramus communicans fibularis nerve, and the external 

 or ?hort saphenous nerve. These, except the last named, have been 

 already described. 



