EXTERXAL PLAXTAR 593 



(Gj The malleolar or internal malleolar branches aro distributed, as the 

 name implietJ, over the internal nialleolu!?, anastoniosinj; witli tlie other arteries 

 entering into the retiforni plexus of vessels over that j)ortion of bone. In their 

 eourse to tlie malleolus, they run l)eneath the flexor loiigus digitorum and tibialis 

 posticus muscles. 



(7) The calcanean or internal calcanean branch is distributed to the soft 

 parts over the inner side of the calcaneum. This branch — or, as is frequently the 

 case, branches — comes off from the posterior tibial just before its bifurcation, and 

 anastomoses with the internal malleolar and peroneal arteries (fig. 379j. 



(8) The terminal branches are the external and internal plantar arteries. 



THE EXTERNAL PLANTAR ARTERY 



The external plantar artery — the larger of the two branches into which the 

 posterior tit>ial divides beneath the internal annular ligament — passes at first 

 obliquely forwards and outwards across the sole of the foot to the base of the fifth 

 metatarsal bone, where it makes a bend forwards and inwards, and, sinking deeply 

 into the foot, terminates at the proximal end of the first interosseous space by 

 anastomosing Avith the communicating branch of the dorsal artery of the foot. In 

 its course to the fifth metatarsal bone the artery runs in a more or less straight line 

 oblicjuely across the foot; whilst its deep portion, extending from the fiftli metatarsal 

 bone to the proximal end of the first interosseous space, forms a slight curve with 

 tlie convexity forwards, and is know^n as the plantar arch. The plantar arch is 

 comparable to the deep palmar arch formed by the deep branch of the ulnar 

 anastomosing with the radial through the first interosseous space. This homology 

 is at times more complete in that the communicating branch of the dorsalis pedis, 

 the homologue of tlie radial in the upper limb, takes the chief share in forming 

 the arch. The external plantar artery is accompanied by two veins. The course 

 of the artery is indicated by a line drawn across the sole of the foot from a point 

 midway between the tip of the internal malleolus and the greater tuliercle of the 

 calcaneum to the base of the fifth metatarsal bone, and thence forwards and 

 inwards to the posterior part of the ball of the great toe. 



Relations. — In the first part of its course from the inner ankle to the base 

 of the fifth metatarsal bone, the artery is covered successively by the abductor 

 hallucis and the flexor brevis digitorum, by which it is separated from the plantar 

 fascia, and may be slightly overlapped in muscular subjects by the abductor minimi 

 digit!. As it approaches the base of the fifth metatarsal bone, it lies, as it turns 

 forwards and inwards before sinking into the foot, in the interspace between the 

 riexor brevis digitorum and the abductor minimi digiti. and is here only covered 

 by the skin and superficial fascia, and the plantar fascia. It lies upon the cal- 

 caneum, the flexor aceessorius. and the flexor brevis minimi digiti. It is accom- 

 jianied by the external plantar nerve, the smaller of the two divisions into which 

 the posterior tibial nerve divides. In this part c»f its course it gives off small 

 branches to the contiguous muscles and to the heel. 



In the second part of its course the artery, which is here known as the 

 ])lantar arch, sinks into the sole, and is covered, in addition to the skin, superficial 

 fascia, plantar fascia, and flexor lirevis digitorum, by the tendon of the flexor 

 longus digitorum, the lumbricales, branches of tlie internal plantar nerve, and tin- 

 adductor hallucis. It lies upon the proximal ends of the second, tliird, and fourth 

 metatarsal bones and the cnrresiionding interosseous muscles. 



The branches of the external plantar artery are: — ( 1 ) Mu.scular; (2) cal- 

 caneal; (3) cutaneous; (4 j anastomotic; (5) articular; (0) posterior perforating; 

 and (7) digital. 



(1) The muscular branches of the external plantar are distributed to the 

 contiguous muscles; in the first part of its course to the flexor brevis digitorum, 

 and the aceessorius; as it makes its bend into the sole, Xo the muscles of the little 

 toe; and. as it forms the plantar anh. to the interossei. flexor brevis hallucis, and 

 adductor hallucis. 



(2) The calcanean are two or three small branches which are distrilnited over 

 38 



