730 THE NERVOUS SYSTEM. 



NERVUS PERON.EUS COMMUNIS. 



The common peroneal (O.T. external popliteal) nerve arises from the posterior 

 part of the sacral plexus from the fourth and fifth lumbar and first two sacral 

 nerves. Incorporated with the sciatic nerve in the buttock and proximal part of 

 the thigh, it passes distally from the bifurcation of that nerve through the popliteal 

 fossa, to its termination at a point about an inch distal to the head of the fibula. It 

 is concealed at first by the biceps muscle. Following the tendon of that muscle, it 

 passes obliquely through the proximal and lateral part of the popliteal fossa and 

 over the lateral head of the gastrocnemius muscle to the posterior aspect of the 

 head of the fibula. In the distal part of its course it is quite superficial, but at 

 its termination it is covered by the peronseus longus muscle. 



Collateral Branches. These are divided into two sets : (a) Nerves arising from 

 the roots or trunk of the nerve while it is in combination with the tibial nerve in 

 the sciatic trunk. These have been already described, as a muscular branch to the 

 short head of the biceps, and an articular branch to the knee-joint. (6) Nerves 

 arising in the popliteal fossa. These are cutaneous branches, viz., the lateral sural 

 nerve or lateral cutaneous nerve of the calf and the peroneal anastomotic ramus. 



N. Cutaneus Surae Lateralis. The lateral sural branch is irregular in size 

 and distribution, and may be represented by two or more branches (Fig. 628, p. 731). 

 Arising from the common peroneal nerve in the popliteal fossa, often in common 

 with the succeeding nerve, it pierces the deep fascia over the lateral head of the 

 gastrocnemius, and is distributed to the skin on the lateral aspect of the back of 

 the leg in the proximal two-thirds. The extent of its distribution varies with 

 that of the posterior cutaneous nerve of the thigh and the nervus suralis. 



Ramus Anastomoticus Peronseus. The peroneal anastomotic nerve (O.T. com- 

 municans fibularis), arising in the popliteal fossa, passes over the lateral head of 

 the gastrocnemius beneath the deep fascia to the middle third of the leg, where 

 it assists in forming the nervus suralis by its union with an anastomotic (communi- 

 cating) branch of the tibial nerve called the medial sural nerve or medial cutaneous 

 nerve of the calf. In many cases the two branches do not unite. In such cases 

 the peroneal anastomotic nerve may be limited in its distribution to the skin of 

 the lateral side of the leg, heel, and ankle, or it may be distributed to the area 

 usually supplied by the nervus suralis. 



Terminal Branches. The terminal branches of the common peroneal nerve 

 are three in number : recurrent tibial, deep peroneal (O.T. anterior tibial), and 

 superficial peroneal (O.T. musculo-cutaneous). They arise just distal to the head of 

 the fibula, and are directed forwards, diverging in their course, beneath the peroneus 

 longus muscle. 



The recurrent tibial nerve is the smallest branch. Passing forwards under cover 

 of the origin of the peronseus longus and the extensor digitorum longus muscles, it 

 divides, distal to the lateral condyle of the tibia, into branches which supply the 

 proximal fibres of the tibialis anterior muscle, the proximal tibio-fibular articula- 

 tion, and the knee-joint. 



NERVUS PERONSEUS PROFUNDUS. 



The deep peroneal nerve (O.T. anterior tibial) passes obliquely distally, 

 under cover of the peronseus longus, extensor digitorum longus, and extensor hallucis 

 longus muscles, to the front of the leg. In its course it is deeply placed upon the 

 interosseous membrane and the distal part of the tibia, in company with the 

 anterior tibial artery. At the ankle it lies under cover of the transverse ligament 

 of the leg and the tendon of the extensor hallucis longus, and, crossing the ankle- 

 joint, it divides on the dorsum of the foot into its terminal branches. 



1. Collateral Branches (in the leg). These are given off to the muscles between 

 which the deep peroneal nerve passes, namely : tibialis anterior, extensor hallucis 

 longus, extensor digitorum longus, and peronseus tertius. A fine articular branch 

 surmlies the ankle-ioint. 



