INTERNAL POPLITEAL NERVE 817 



The INTERNAL POPLITEAL NERVE, formed of fil)res from tlie fourth aiul 

 fifth himbar and tlie lirst, second, and tliird sacral nerves, is larger than the external 

 ])o})liteal nerve; it runs downwards, following the same direction as the great sciatic, 

 to reach the lower border of the popliteus muscle, ■where it is continued into the 

 posterior tibial nerve. In this course it occu])ies the middle vertical diameter of 

 the popliteal space, and is the most superficially i)laced of the important contents 

 of tiiat sjjace. It is overlapped l)y the hamstring muscles above and by the heads 

 of the gastrocnemius below; but is covered only by the skin and fasciae for about 

 two inches above the line of the knee-joint. The popliteal vein intervenes between 

 the internal popliteal nerve and the artery, and the nerve is on a })lane superficial 

 to the vessels. In the up]>er i)art of the popliteal space the vessels are internal to 

 the nerve; at the level of the knee-joint they are immediately in front of the nerve; 

 and at tlie lower part of the space they are placed external to it. 



Branches. — The branches of the internal popliteal nerve may be classified into 

 cutaneous, articular, musculai', and terminal. 



(1) The cutaneous branch, the nervus communicans tibialis, containing 

 fibres from the first and second sacral nerves, arises from the internal popliteal 

 al)Out the centre of the popliteal space, and runs vertically downwards, under cover 

 of the deep fascia, to reach the interval between the two heads of the gastrocnemius; 

 then, inclining a little outwards, it pierces the deep fascia, and unites with the 

 conmumicans fibularis to form the short saphenous nerve. The external or short 

 saphenous nerve is formed alwut the middle of the calf (sometimes higher up or 

 lower d(jwn), and runs downwards and out^vards, accom]ianied by the vein of the 

 same name, to reach the interval betAveen the external malleolus and the calcaneum. 

 It crosses superficial to the external annular ligament, and then runs forwards along 

 the outer border of the foot, supplying numerous twigs to the integument of the 

 region. Having communicated Avith the external branch of the musculo-cutaneous, 

 it terminates by supplying the integument on the outer side of the little toe. 



Varieties. — In a large number of cases the distribution of this nerve is much more extensive. 

 It may supply the fiftli and fourth toes and the outer border of the third. In some cases the 

 communicans fibularis does not join the communicans tibialis, but ends independently in the 

 intci-'uments of the calf 



(2) The muscular branches of the internal popliteal nerve are distributed to 

 the gastrocnemius, soleus, plantaris, and popliteus muscles. There is a separate 

 branch for each head of the gastrocnemius, containing fibres from the first and 

 second sacral nerves. The branches to the plantaris and popliteus muscles are 

 formed of fibres from the fourth and fifth lumbar and first sacral nerves. The 

 l)ranch to the popliteus arises lower doAvn than the other branches. It crosses the 

 superficial surface of the popliteal artery to reach the outer side of that vessel, runs 

 downwards on the posterior surface of the popliteus, and winds round the lower 

 border of that muscle to gain its deep or anterior surface, where it ends in the mus- 

 cular substance; before it turns round the lower border of the muscle, it gives a 

 branch to the superior tibio-fibular articulation, another to the tibia along the medul- 

 lary artery, and a long branch to the interosseous membrane; the latter gives twigs 

 to the anterior and posterior tibial arteries and then runs down in the interosseous 

 membrane and ends in the inferior tibiofibular articulation. The nerve to the 

 soleus is relatively large, it crosses the plantaris to gain the posterior surface of the 

 soleus carrying fil>res of the fifth lumbar and the first and second sacral nerves. 



(3j The articular branches are three in numlier, and accompany the superior 

 and inferior internal articular and the azygos branches of the ])Opliteal artery, to be 

 distril)uted to tlie knee-joint. 



The POSTERIOR TIBIAL NERVE contains fibres derived from the fourth and 

 fifth lumbar and llie first and sec-ond sacral nerves; it is the terminal branch of the 

 internal popliteal, or rather the direct continuation of that nerve. It runs down- 

 wards with an inclination inwards to reach the interval between the inner malleolus 

 and the os calcis, and, having passed under cover of the origin of the abductor 

 hallucis muscle, terminates by dividing into the internal and external plantar 

 nerves, at a point midway between the tip of the internal malleolus and the most 

 prominent part of theos calcis. In the upjter ]>art of its course it is covered by the 



