EXTERNAL POPLITEAL NERVE 815 



trunk. One of these, the external cutaneous nerve, whicli contains filjres fnjm the 

 fifth himbar and the first and second sacral nerves is distributed to the skin cover- 

 ing; tlie (lUtHr and U])per i)art of the leg. The other branch, the nervus commu- 

 nicans peronei or fibularis, containing fibres from the same roots, runs downwards 

 and inwards beneath the deep fascia, and joins the nervus communicans tibialis 

 to form the external or short saphenous nerve (page 817). 



(3) The recurrent articular nerve ends principally in the upi)er ])art of tlie 

 tibialis anticus muscle. A few tiiK- filaments accompany the anterior tibial recur- 

 rent artery to the front of the knee-joint, some pass the superior tiltio-fibular articu- 

 lation, and others to the head of the tibia. 



(4) The musculo-cutaneous nerve, containing fibres from the fourth and fifth 

 lumbar and the fir.<t sacral nerves, is directed dowuwards through the substance 

 of the peroneus longus, and is afterwards placed between the peronei and extensor 

 longus digitorum. Having given off branches to supply these muscles, it divides 

 into an external and an internal branch; these branches pierce the deep fascia in 

 the line of the intermu.^cular septum between the peronei and the extensor grou{> 

 of muscles. The external branch runs downwards, in front of the anterior annular 

 ligament, and divides into the following V)ranches: a tAvig which communicates with 

 the short saphenous; a branch which divides to sup])ly the adjacent sides of the 

 fourth and fifth toes; and a branch whidi communicatis with the internal division 

 of the musculo-cutaneous nerve. The internal branch crosses the anterior annular 

 ligament about an inch to the inner side of the external branch, and divides into 

 four branches: the first of these communicates with the external branch, forming 

 with it a nerve Avhich bifurcates to supply the adjacent sides of the third and fourth 

 toes; the second divides to be distributed to the contiguous sides of the second and 

 third toes; the third communicates with the internal terminal branch of the anterior 

 tibial at the cleft between the great and second toes; and the fourth supplies the 

 inner border of the great toe. 



In their course across the dorsum of the foot the branches of the musculo- 

 cutaneous nerve pass beneath the dorsal venous arch, and from the two main divi- 

 sions of the nerve a number of collateral twigs are given off, which supply the 

 integument of the lower part of the front of the leg and the dorsum of the foot. 



(5) The anterior tibial nerve, formed from fibres of the fourth and fifth 

 lumbar and the first sacral nerves, pierces the intermuscular septum between the 

 peronei and extensors, and, having traversed the upper fibres of the extensor longus 

 digitorum, runs downwards on the interosseous membrane between the last-named 

 muscle and the tibialis anticus; lower down it is placed between the tibialis anticus 

 and the extensor longus hallucis. It crosses beneath the extensor longus hallucis, 

 passes under cover of the anterior annular ligament, and temiinates in front of the 

 bend of the ankle by dividing into an external and an internal branch. In this 

 course it is placed external to the anterior tibial arter}^ in the upper third of the 

 leg; it lies on the anterior surface of that vessel in the middle third, and in the 

 remainder of its course it is again external to the artery. 



Branches. — In addition to the two terminal branches above mentioned, the 

 anterior til>ial nerve gives oflf an articular twig to the ankle-joint, and branches to 

 supply the tibialis anticus, extensor longus hallucis, extensor longus digitorum, 

 and jjeroneus tertius. The branches destined for the two latter muscles arise in 

 conmion, and take the form of a long slender nerve which runs along the inner side 

 of the muscles. su]tplyintr them with numerous twigs. 



The external branch is directed outwards under cover of the extensor brevis 

 digitorum, and, having supplied that muscle, ends in twigs which are distributed 

 to the tarsal articulations. This nerve presents a gangliform enlargement near its 

 termination, thus resembling the posterior intero.sseous nerve in the superior 

 extremity, and from its terminal branches filaments pass to the interosseous s])aces, 

 where they anastomose with branches of the external jilantar nerve and supjily the 

 tarso-metatarsal articulations and one or more dorsal interossei muscles. 



The internal branch is directed forAvards towards the interval between the first 

 and second toes, Avhere it is joined by a tAvig from tiie musculo-cutaneous, and then 

 divides to su])i)ly the contiguous margins of the above-mentioned toes. In its 

 course on the dorsum pedis it lies to the outer side of the dorsal artery of the foot. 



