THE POPLITEAL, TIBIA L, AND PLANTAR NERVES. 863 



The Internal Popliteal Nerve, the larger of the two terminal branches of the 

 great sciatic, descends along the back part of the thigh, through the middle of 

 the popliteal space, to the lower border of the Popliteus muscle, where it passes 

 with the artery beneath the arch of the Soleus and becomes the posterior tibial. 

 It is overlapped by the hamstring muscles above, and then becomes more super- 

 ficial, and lies to the outer side of, and some distance from, the popliteal vessels ; 

 opposite the knee-joint it is in close relation with the vessels, and crosses to the 

 inner side of the artery. Below, it is overlapped by the Gastrocnemius. 



The branches of this nerve are articular, muscular, and a cutaneous branch, 

 the commuiii<-<nix /><>j>!/'t>-i nerve. 



The arti'-al'ir branches, usually three in number, supply the knee-joint: two of 

 these branches accompany the superior and inferior internal articular arteries, 

 and a third, the azygos articular artery. 



The muscular branches, four or five in number, arise from the nerve as it lies 

 between the two heads of the Gastrocnemius muscle ; they supply that muscle, 

 the Plantaris, Soleus, and Popliteus. The filaments which supply the Popliteus 

 turn round its lower border and are distributed to its deep surface. 



The eommunieans poplitei descends between the tAvo heads of the Gastrocne- 

 mius muscle, and about the middle of the back of the leg pierces the deep fascia, 

 and joins a communicating branch (communicans peronef) from the external 

 popliteal nerve to form the external or short saphenous (Fig. 509). The exter- 

 nal saphenous nerve, formed by the cutaneous branches of the internal and 

 external popliteal nerves, passes downward and outward near the outer margin of 

 the tendo Achillis, lying close to the external saphenous vein, to the interval 

 between the external malleolus and the os calcis. It winds round the outer mal- 

 leolus, and is distributed to the integument along the outer side of the foot and 

 little toe, communicating on the dorsum of the foot with the musculo-cutaneous 

 nerve. In the leg its branches communicate with those of the small sciatic. 



The Posterior Tibial Nerve (Fig. 510) commences at the lower border of the 

 Popliteus muscle, and passes along the back part of the leg with the posterior 

 tibial vessels to the interval between the inner malleolus and the heel, where it 

 divides into the external and internal plantar nerves. It lies upon the deep 

 muscles of the leg, and is covered in the upper part by the muscles of the calf, 

 lower down by the skin and fascia. In the upper part of its course it lies to the 

 inner side of the posterior tibial artery, but it soon crosses that vessel, and lies to 

 its outer side as far as the ankle. In the lower third of the leg it is placed 

 parallel with the inner margin of the tendo Achillis. 



The branches of the posterior tibial nerve are muscular, plantar cutaneous, and 

 articular. 



The muscular branches arise either separately or by a common trunk from the 

 upper part of the nerve. They supply the Tibialis posticus, Flexor longus digito- 

 rum, and Flexor longus hallucis muscles, the branch to the latter muscle accom- 

 panying the peroneal artery. A branch is also given to the Soleus. 



The plantar cutaneous branch perforates the internal annular ligament and 

 supplies the integument of the heel and inner side of the sole of the foot. 



The arti-ulnr branch is given off just above the bifurcation of the nerve and 

 supplies the ankle-joint. 



The internal plantar nerve (Fig. 511), the larger of the two terminal branches 

 of the posterior tibial, accompanies the internal plantar artery along the inner side 

 of the foot. From its origin at the inner ankle it passes beneath the Abductor 

 hallucis, and then forward between this muscle and the Flexor brevis digitorum, 

 divides opposite the bases of the metatarsal bones into four digital branches, and 

 communicates with the external plantar nerve. 



Branches. In its course the internal plantar nerve gives off cutaneous 

 branches, which pierce the plantar fascia and supply the integument of the sole 

 of the foot ; muscular branches, which supply the Abductor hallucis and Flexor 

 brevis digitorum ; articular branches, to the articulations of the tarsus and meta- 



