558 A MANUAL OF ANATOMY 



nerve to the outer side of the Httle toe. Sometimes, however, the 

 deep division of the nerve supphes all seven interosseous muscles. 

 In all cases the nerves enter the muscles on their plantar aspects. 



Action — Plantar Interossei. — These are adductors, the toes which 

 they adduct being the third, fourth, and fifth. Dorsal Interossei. — 

 These are abductors, the toes which they abduct being the second, 

 third, and fourth. 



In speaking of adduction and abduction in the case of the foot, 

 reference is made to an imaginary line passing through the centre 

 of the second toe, adduction being movement towards that line, 

 and abduction movement from it. 



The first and second dorsal interossei, acting both upon the second 

 toe, abduct it from the imaginary line passing through its centre, 

 the first abducting it to the inner side and the second to the outer 

 side. The third and fourth dorsal interossei abduct the third and 

 fourth toes. 



The interosseous muscles, aided by the lumbricales, also act as 

 follows : (i) they flex the metatarso-phalangeal joints of the four 

 outer toes, and (2) they extend the interphalangeal joints of these 

 toes. 



The tendons of the peroneus longus and tibialis posticus have 

 been already described. 



Plantar Nerves. — The plantar nerves are two in number, internal 

 and external. They are the terminal branches into which the 

 posterior tibial nerve divides on a level with the lower border of 

 the internal annular ligament, though the division frequently 

 takes place on a level with the upper border of that ligament, or 

 at some point beneath it. The internal plantar is the larger of 

 the two nerves, and it accompanies the internal plantar artery, 

 which is the smaller of the two plantar arteries. The external 

 plantar nerve accompanies the external plantar artery. 



Internal Plantar Nerve. — This nerve has a wider cutaneous, but 

 a more limited muscular, distribution than the external plantar. 

 From its origin it passes forwards on the outer side of the internal 

 plantar artery, being at first under cover of the abductor hallucis, 

 and subsequently lying between that muscle and the flexor brevis 

 digitorum. About the middle (in length) of the foot it divides 

 into its terminal branches. 



Branches. — ^These are muscular, articular, plantar cutaneous, and 

 digital. 



The muscular branches supply the abductor hallucis and flexor 

 brevis digitorum. 



The articular branches are distributed to the astragalo-navicular 

 and naviculo-cuneiform articulations. 



The plantar cutaneous branches are distributed to the integu- 

 ment of the inner half of the sole. 



The digital branches are four in number, and are named first, 

 second, third, and fourth from within outwards. The first is a 

 single nerve, but the other three are compound. The first digital 



