1342 HUMAN ANATOMY. 



small size and of varying number. There are usually two, an upper and a lower, and these 

 break up into small filaments which inosculate with the lower articular fibres of the external 

 popliteal, forming the popliteal plexus of Riidinger. The upper or azygos branch usually 

 pierces the posterior ligament of the joint, while the lower accompanies the inferior internal 

 articular artery. When a third is present it accompanies the superior internal articular artery. 

 From the popliteal plexus a number of fine filaments are furnished to the posterior portion of 

 the knee joint and an occasional twig enters the popliteus muscle by piercing its posterior 

 surface. 



b. The muscular branches (rr. musculares) comprise two sets, those given off from the 

 part above the division of the sciatic nerve and those given off below. The former have been 

 described on page 1333. The latter consist of a series of five twigs which innervate the 

 gastrocnemius, the soleus, the plantaris and the popliteus. 



The nerves to the gastrocneniiics, soleus and plantaris consist of two stout nerve trunks, 

 an upper and a lower. The upper arises in the middle of the popliteal space and enters the 

 lateral aspect of the inner head of the gastrocnemius. The lower arises a short distance below 

 the upper and, frequently combined with the nerve to the plantaris, divides into two branches, 

 a shorter for the outer head of the gastrocnemius, and a longer, which enters the superior bor- 

 der of the soleus, the upper part of which muscle it supplies. From the nerve to the plantaris 

 is furnished a filament to the knee joint. 



The nerve to the popliteus is a complex structure, with a distribution much wider 

 than is implied in its name. After reaching the lower margin of the popliteus muscle the 

 nerve turns forward, ascends between the anterior aspect of the muscle and the tibia, and 

 enters the anterior surface of the popliteus. A branch supplies the periosteum of the tibia and 

 then enters the nutrient foramen of that bone. Another, the interosseous branch (n. interosseus 

 cruris) courses first posterior to and then between the layers of the interosseous membrane 

 almost to its lower margin. Terminal fibres are distributed to the periosteum of the tibia and 

 to the inferior tibio-fibular articulation. Other filaments reach the tibialis posticus muscle and 

 the superior tibio-fibular articulation. 



c. The cutaneous branch is the tibial coniinunicathig nerve. 



The tibial communicating nerve or n. tibialis covwiunicans (n. cutaneus surae medialis) 

 (Fig. 1 1 19) arises in the upper portion of the popliteal space, through which it passes, posterior 

 to the internal popliteal nerve, to the fissure between the heads of the gastrocnemius. In 

 company with the external saphenous vein, the nerve descends in this interval to the tendo 

 Achillis and, after piercing the deep fascia at about the middle of the leg, is joined by the 

 peroneal communicating nerve, the fusion resulting in the external or short saphenous nerve 

 (n. suralis). This joint nerve (Fig. 1119) courses down the postero-lateral aspect of the lower 

 part of the leg, passes posterior to and beneath the external malleolus in company with the 

 external saphenous vein and follows a course obliquely downward and forward along the 

 lateral margin of the foot to the dorsal aspect of the outer side of the fifth toe, at the far end 

 of whose distal phalanx the nerve terminates. In its course through the leg and foot it supplies 

 sensory twigs to the postero-lateral part of the lower third of the leg, the region over the 

 external malleolus, the lateral portion of the heel (rr. calcanei laterales), the dorso-lateral 

 portion of the foot (n. cutaneus dorsalis lateralis) and the outer half of the dorsum of the fifth 

 toe. Twigs are furnished to the ankle, and to the astragalo-calcanean and possibly other inter- 

 tarsal articulations. In the foot it communicates with the anterior tibial nerve. 



Variations. — The point of union of the two tributaries of the external saphenous is subject 

 to wide variations, sometimes being high in the popliteal space and sometimes there being no 

 union at all, in the latter instance the nerve which reaches and supplies the foot usually being 

 the n. communicans tibialis. In one specimen found in the anatomical rooms of the University 

 of Pennsylvania the great sciatic nerve divided just below the margin of the gluteus maximus. 

 The n. communicans fibularis arose in the middle of the thigh and the n. communicans tibialis 

 in the popliteal space. Union took place 3 cm. below the origin of the n. communicans tibialis, 

 the n. communicans fibularis sending a few fibres across to the internal popliteal nerve before 

 entering the external saphenous. In another cadaver in the same laboratory the two tributa- 

 ries arose 3 cm. apart from each other about 10 cm. above the knee, the n. communicans tib- 

 ialis arising the higher and piercing the inner head of the gastrocnemius before joining the n. 

 communicans fibularis. Variations in distribution may occur, the nerve sometimes supplying 

 the dorsal aspect of two and one-half digits, under such circumstances the n. communicans 

 fibularis usually being of increased size. The nerve may terminate in the foot and not have any 

 digital distribution. 



d. The Posterior Tibial Nerve. 



The posterior tibial nerve (n. tibialis) (Fig. 1119) is the direct continuation 

 of the internal popHteal and begins at the lower border of the popliteus muscle. It 

 extends downward, in a sheath shared by the posterior tibial vessels, between the 

 superficial and deep muscles of the posterior portion of the leg. Anterior to it are 



