POSTERIOR TIBIAL NERVE. 423 



by the side of the external saphenous vein which it accompanies to 

 the foot. At the lower part of the leg it winds around the outer 

 malleolus, and is distributed to the outer side of the foot and of the 

 little toe, communicating with the external peroneal cutaneous nerve, 

 and sending numerous filaments to the integument of the heel and of 

 the sole of the foot. 



The POSTERIOR TIBIAL NERVE is continued along the posterior 

 aspect of the leg from the lower border of the popliteus muscle to 

 the posterior part of the inner ankle, where it divides into the 

 internal and external plantar nerve. In the upper part of its course 

 it lies to the outer side of the posterior tibial artery; it then becomes 

 placed superficially to that vessel, and at the ankle is again situated 

 to its outer side ; in the lower third of the leg it lies parallel with the 

 inner border of the tendo Achillis. 



The Branches of the posterior tibial nerve are three or four mus- 

 cular twigs to the deep muscles of the posterior aspect of the leg ; 

 the branch to the flexor longus pollicis accompanies the fibular 

 arteiy ; one or two filaments which entwine around the artery and 

 then terminate in the integument :* and some cutaneous branches 

 which pass downwards upon the inner side of the os calcis and are 

 distributed to the integument of the heel. 



The Internal plantar nerve, larger than the external, crosses the 

 posterior tibial vessels to enter the sole of the foot, where it lies in 

 the interspace between the abductor pollicis and flexor brevis digi- 

 torum ; it then enters the sheath of the latter muscle, and divides 

 opposite the bases of the metatarsal bones into three digital branches ; 

 one to supply the adjoining sides of the great and second toe ; the 

 second to the adjoining sides of the second and third toe ; and the 

 third to the third and fourth toes. The distribution is precisely 

 similar to that of the digital branches of the median nerve. 



In its course the internal plantar nerve gives off cutaneous branches 

 to the integument of the inner side and sole of the foot ; muscular 

 branches to the muscles forming the inner and middle group of the 

 sole; a digital branch, to the inner, border of the great toe; and 

 articular branches to the articulations of the tarsal and metatarsal 

 bones. 



The External plantar nerve, the smaller of the two, follows the 

 course of the external plantar artery to the outer border of the 

 musculus accessorius, beneath which it sends several large mus- 

 cular branches to supply the abductor pollicis and the articulations 

 of the tarsal and metatarsal bones. It then gives branches to the 

 integument of the outer border and sole of the foot, and sends for- 

 ward two digital branches to supply the little toe and one half the 

 next. 



* It is extremely interesting in a physiological point of view, to observe the mode of 

 distribution of these filaments. I have traced them in relation with several, and I have 

 no doubt that they exist in connexion with all the superficial arteries. They seem to 

 be the direct monitors to the artery of the presence or approach of danger. 



