840 HUMAN ANATOMY. 



origin a larger branch, the anasto'motic branch, which passes beneath the abductor hallucis to 

 gain the upper border of that muscle, along which it courses forward, giving of? numerous 

 branches to the abductor and the adjacent integument and anastomosing with the tarsal and 

 metatarsal branches of the dorsalis pedis. More distally it gives off from its outer surface a 

 varying number of slender superficial digital branches, which pass obliquely forward and out- 

 ward across the sole of the foot to anastomose with one or more of the plantar interosseous 

 branches from the plantar arch. 



Variations. — Occasionally the superficial digital branches of the internal plantar arise from 

 a common stem which anastomoses with a branch from the external plantar to form a superfi- 

 cial plantar arch beneath the superficial fascia. This is the equivalent of the superficial palmar 

 arch of the hand. 



7. The External Plantar Artery. — The external plantar artery (a. plantaris 



lateralis) (Fig. 740) is the larger of the terminal branches of the posterior tibial. It 

 passes forward and outward across the sole of the foot, at first between the flexor 

 brevis digitorum and the flexor accessorius, and then in the interval between the flexor 

 brevis digitorum and the abductor minimi digiti. Opposite the base of the fifth meta- 

 tarsal bone it turns somewhat abruptly inward and again crosses the sole of the foot, 

 forming the plantar arch (arcus plantaris), which terminates at the proximal end of 

 the first intermetatarsal space by uniting with the communicating branch from the 

 dorsalis pedis. 



Relations. — In the first part of its course the external plantar lies beneath the 

 abductor hallucis and the flexor bre\'is digitorum, but as it approaches the fifth meta- 

 tarsal it becomes more superficial, being covered only by the skin and the superficial 

 and plantar fasciae. It rests upon the flexor accessorius and the flexor brevis minimi 

 digiti, and is accompanied by the external plantar nerve. 



The plantar arch, on the contrary, occupies a much deeper position. It passes 

 beneath the tendons of the flexor longus digitorum, the lumbricales, and the oblique 

 portion of the adductor hallucis, resting upon the proximal ends of the second, third, 

 and fourth metatarsals and upon the interosseous muscles which occur between those 

 bones. 



Branches. — The external plantar artery gives rise to (a) numerous muscular branches 

 which supply the various muscles of the plantar surface of the foot, and in its first part to 



{b) Cutaneous branches which supply the skin over the sole and outer border of the foot, 

 some of them forming anastomoses with branches of the tarsal and metatarsal branches of the 

 dorsalis pedis. In addition, there are given off from the first portion of the artery — 



(r) Calcaneal branches, one or more in number, which arise near the commencement of 

 the external plantar and ramify over the inner surface of the os calcis, anastomosing with the 

 internal calcaneal branches of the posterior tibial. 



From the plantar arch a number of vessels are given off. 



{d) The articulating branches are given off from the posterior or concave surface of the 

 arch and supply the tarsal articulations. 



{e) The posterior perforating branches, four in number, arise either from the plantar arch 

 or from the plantar digital branches of the fourth intermetatarsal space. They ascend in the 

 intermetarsal spaces between the heads of the dorsal interosseous muscles and terminate by inos- 

 culating with the first, second, and third dorsal interosseous arteries. The branch which passes 

 through the first intermetatarsal space is much larger than the rest and inosculates with the dor- 

 salis pedis artery ; it is sometimes regarded as the terminal branch of that vessel. 



(/) The plantar interosseous arteries f aa. metatarsae plantares) are five in number, and are 

 usually numbered in succession from the outer side of the foot inward, — that is to say, in the 

 opposite direction to the intermetatarsal spaces in which they lie. The first arises just where 

 the external plantar artery is bending inward to form the plantar arch and passes forward 

 along the inner border of the abductor minimi digiti, later crossing over the flexor brevis minimi 

 digiti to reach the outer surface of the little toe, along which it runs. 



The second, third, and fou7-th plantar interosseous arteries arise in succession from the 

 plantar arch as it crosses the fourth, third, and second intermetatarsal spaces, and pass forward, 

 resting upon the interosseous muscles and covered by the tendons of the flexor longus digitorum 

 and the lumbricales, and more distally by the transverse adductor of the great toe. Just before 

 reaching the line of the metatarso-phalangeal articulations each artery gives off an anterior per- 

 forating branch, which passes dorsally to commimicate with the corresponding dorsal interos- 

 seous artery, and then divides into two plantar digital branches, which pass onward upon the 

 adjacent sides of neighboring digits. 



