952 THE NERVOUS SYSTEM 



accessorius) , and deep to the flexor digitorum brevis. At its termination it lies in 

 the interval between the flexor digitorum brevis and abductor digiti quinti. 



Branches. From the trunk of the lateral plantar nerve muscular and articular 

 branches are given off. 



The muscular branches arise from the commencement of the nerve and are dis- 

 tributed to the abductor digiti quinti and quadratus plantse. 



The articular branches supply the calcaneo-cuboid joint. 



The superficial branch supplies muscular filaments to the flexor digiti quinti 

 brevis, the third plantar and fourth dorsal interosseous muscles, and divides into two 

 common plantar digital nerves, each of which subdivides to form proper plantar 

 digital nerves. The outer of the two branches supplies the outer side of the fifth 

 digit ; the inner communicates with the outer digital branch of the medial plantar 

 nerve (fig. 696) and divides into proper plantar digital nerves for the adjacent sides 

 of the fourth and fifth digits. The digital branches of the superficial division of the 

 lateral plantar, like those of the medial plantar, supply the skin of the toes and the beds 

 of the nails, and are associated with numerous Pacinian corpuscles. 



The deep branch passes forwards and inwards into the deep part of the sole with 

 the plantar arterial arch. It runs deep to the quadratus plantse, the long flexor 

 tendons and the lumbricals, and the oblique adductor of the great toe. It lies, there- 

 fore, immediately beneath the bases of the metatarsal bones and it supplies the fol- 

 lowing muscular and articular branches: 



Muscular branches to the outer three lumbricals, the interossei of the inner 

 three inter-metatarsal spaces, and the transverse and oblique adductor muscles 

 of the great toe. 



Articular branches to the intertarsal and to the tarso-metatarsal joints and not 

 uncommonly to the metatarso-phalangeal joints also. Filaments from the deep 

 branc-h frequently pass through the interosseous spaces and communicate with 

 the interosseous branches of the deep peroneal (anterior tibial) nerve. 



The Common Peroneal (External Popliteal) Nerve. At the apex of the pop- 

 liteal space, where the two component parts of the sciatic trunk usually become 

 distinct, the external portion receives the name n. perorueus communis. It descends 

 along the posterior border of the biceps femoris, which forms the upper part 

 of the outer boundary of the space (fig. 695). It leaves the space at the external 

 lateral angle, crosses the plantaris, the outer head of the gastrocnemius, the pop- 

 liteus, and the inferior external artery, and descends behind the upper part of the 

 soleus, to the neck of the fibula, where it turns forwards between the peroneus longus 

 and the bone, and breaks up into its three terminal branches, the recurrent articular, 

 the superficial peroneal (musculo-cutaneous), and the deep peroneal (anterior tibial) 

 nerves (fig. 697). 



Upper branches. While it is in the popliteal space the peroneal (external popliteal) 

 nerve gives off two articular branches and a cutaneous branch. The upper articular 

 branch accompanies the superior external articular artery. The lower articular 

 branch passes down with the trunk of the nerve, across the plantaris and the outer 

 head of the gastrocnemius, and it joins the lower external articular artery behind 

 the tendon of the biceps femoris. Both the upper and lower articular branches pierce 

 the ligaments and are distributed in the interior of the joint. 



The cutaneous branch (communicans fibularis), lateral sural cutaneous, is 

 extremely variable both as to the number of its branches and as to the place of its 

 anastomosis with the medial sural cutaneous. Leaving the common peroneal (ex- 

 ternal popliteal) in the popliteal space, it descends between the deep fascia and the 

 external head of the gastrocnemius to the middle of the calf, where it pierces the fascia 

 and unites with the medial sural cutaneous to form the sural (external saphenous) 

 nerve. In its course it may give off no branches; or it may give off several, some 

 of which supply the skin of the back of the leg, while one of them, the peroneal 

 anastomotic branch, unites with the medial sural cutaneous to form the sural (short 

 saphenous) nerve. The junction of the peroneal anastomotic branch with the 

 medial sural cutaneous may take place at any point between the popliteal space and 

 the lower third of the leg. 



The sural (external or short saphenous) nerve is formed by the union of the 

 lateral sural cutaneous nerve either directly, or through a communicating branch, 

 the peroneal anastomotic, with the medial sural cutaneous (fig. 695). It descends 

 along the outer border of the tendo Achillis, giving branches to the lower and outer 



