PEROXEUS BREVIS 393 



tendon in the sole, and where the tendon enters this canal it often contains a 

 sesamoid l>one which jtlays upon the front of the ridge of the cnl)oid bone. 



Nerve-supply. — From the musculo-cutaneous branch of the external popliteal 

 nerve by filaments which enter the deep and posterior asjject of the muscle in its 

 upper third. 



Action. — (1) To extend the ankle-joint; (2) to al)duct the anterior part of the 

 foot; (3) to depress the inner l)order of the foot, and so to evert the sole; (4) by 

 drawing backwards and outwards the base of the first metatarsal bone, it tends to 

 render more concave the antero-posterior and transverse arches of the foot. In the 

 former action it assists the tibialis i>osticus and flexor longus hallucis. 



In walking, it will act with the gastrocnemius and soleus in lifting the heel from 

 the ground, and its tendency to evert the sole and abduct the foot will counteract 

 the opposite tendency of the muscles attached to the tendo Achillis. ^Moreover, the 

 tendenc}' of this latter set of muscles is to press the outer part of the ball of the 

 toes firmly upon the ground. On the other hand, the influence of the peroneus 

 longus in extending the foot is especially exerted upon the ball of the great toe. 

 By the combined action of all these extensors of the ankle the whole of the ball 

 of the foot is pressed evenly upon the ground and firmness of tread secured. 



Relations. — Superficially, the deep fascia, the external annular ligament; and 

 in the sole, the abductor minimi digiti, the adductor hallucis, and long plantar 

 ligament; in front, the peroneus brevis, the extensor longus digitorum, and the 

 musculo-cutaneous nerve; behind, the soleus and flexor longus hallucis; deeply, 

 the external popliteal nerve which occupies a fibrous canal below the head of the 

 filnila, the ankle-joint, calcaneum, cuboid, and the bases of the second and third 

 metatarsal bones. 



Variations. — Sometimes a second peroneus arises between the peroneus longus and brevis, 

 and sends its tendon to join that of the peroneus longus. A slip may be given to the external 

 annular ligament. The insertion of the muscle may extend to the bases of the adjacent meta- 

 tarsal bones. 



2. PEROXEUS BREVIS 



The peroneus brevis (figs. 292 and 298) — named from its being the shorter of 

 the two fibular muscles — is also a triangular sheet. 



Origin. — (1) The lower two-thirds of the outer (or peroneal) surface of the 

 fiV)ula; (2) the deep fascia of the leg and the intermuscular septa in front and 

 behind. 



Insertion. — (1) The outer part of the base of the fifth metatarsal bone; (2) 

 the outer l)order of the expansion of the tendon of the extensor longus digitorum 

 upon the first phalanx of the little toe. 



Structure. — This is also a penniform muscle. The short fibres pass obliquely 

 downwards to the tendon which lies upon the outer surface of the muscle. It 

 becomes free from fleshy fibres just above the external malleolus where it passes 

 beneath the external annular ligament in the same sheath with the peroneus longus 

 tendon, and after changing its direction, runs forwards and somewhat downwards 

 upon the outer surface of the calcaneum and above the peroneal tubercle. 



Nerve-supply. — The musculo-cutaneous branch of the popliteal nerve by fila- 

 ments which enter the deej) aspect of the muscle about the middle of the leg. 



Action. — (1) Slightly to extend the ankle; (2) to abduct the anterior part of 

 the foot; (3) slightly to elevate the outer border of the foot, and so evert the sole. 



Relations. — Superficially, the peroneus longus, deep fascia of the leg and 

 external annular ligament; in front, the extens(ir longus digitorum and peroneus 

 tertius; Ijehind, the peroneus longus and flexor longus hallucis; deeply, the ankle- 

 joint, calcaneum, and cuboid bones. 



Variations. — The small slip which the tendon sends on to the expansion upon the little toe 

 may be wanting, or it may be inserted into tlie first or even the second phalanx. This slip may 

 be entirely separate, so as to form a fourth peroneus. 



