596 THE ARTERIES 



tiguous joints. At the distal end of the toes they also freel}' anastomose with each 

 other, forming a rete heneatli the pulp and around the matrix of the nail. The 

 digital arteries are each accompanied hy two small veins. 



THE INTERNAL PLANTAR ARTERY 



The internal plantar artery (figs. 378, 379) — the smaller of the two divisions 

 into which the posterior tibial divides at the inner ankle — passes forwards along the 

 inner side of the sole of the foot usually to the first interosseous space, where it ends 

 by anastomosing either with the fifth plantar digital artery (princeps hallucis) 

 derived from the communicating branch of the dorsalis pedis, or with the branch 

 given off by the fifth plantar digital to the inner side of the great toe (figs. 378, 379). 



Relations. — The artery is at first under cover of the abductor hallucis, but 

 afterwards lies in the interval between that muscle and the flexor brevis digitorum. 

 It is covered by the skin and superficial fascia, but not by the plantar fascia, since 

 it lies between the middle and inner portions of that structure. 



The branches of the internal plantar are small and irregular in their origin, 

 course, and distrilmtion. The following are described: — 



(1) The muscular branches supply the abductor hallucis, and flexor brevis 

 digitorum. 



(2) The cutaneous branches supply the skin over the course of the vessel. 



(3) The articular sink deeply into the sole, and supply the articulations on 

 the inner side of the foot, and anastomose with branches of the external plantar 

 artery. 



(4) The anastomotic run beneath the abductor hallucis and round the inner 

 side of the foot, to anastomose with the internal tarsal branch of the dorsalis 

 pedis. 



(5) The superficial digital are very small twigs which accompany the digital 

 branches of the internal i)lantar nerves, and anastomose with the plantar digital 

 arteries in the first, second, and third spaces. At times a twig from one of these 

 branches joins the external plantar artery to form a superficial plantar arch. 



THE ANTERIOR TIBIAL ARTERY 



The anterior tibial artery (fig. 380) — the smaller of the two branches into which 

 the popliteal artery divides at the lower border of the popliteus muscle — at first 

 courses forwards between the two heads of origin of the tibialis posticus, and, after 

 passing between the tibia and filnila above the upper part of the interosseous 

 membrane, runs downwards on the front and outer aspect of the leg, between the 

 anterior muscles, as far as the front of the ankle-joint (fig. 380). Below this spot 

 it is known as the dorsalis pedis. The course of the vessel is indicated by a line 

 drawn from the front of the head of the fibula to a point midway between the two 

 malleoli. 



The artery is accompanied by two veins which conmiunicate with each other at 

 frequent intervals across it. It is also accompanied in the lower three-fourths of its 

 course by the anterior tibial nerve. The nerve, which winds round the head of the 

 fi])ula, and pierces the extensor longus digitorum, first comes into contact with the 

 outer side of the artery somewhere about the upper .third of the leg; then, in 

 the middle third of the leg, it gets a little in front of the artery, and in the lower 

 third again lies to its outer side. 



Relations. — The artery at first lies in the triangle formed by the two heads of 

 the tibialis posticus and the popliteus muscle; and, as it passes through the hole 

 in the interosseous membrane, it has the tibia on one side and the fibula on the 

 other. It is separated from the anterior tibial nerve at its conmiencement by the 

 neck of the fibula and the extensor longus digitorum. This arrangement is 

 homologous with that met with in the forearm in the case of the posterior inter- 

 osseous artery and nerve. 



Posteriorly in its course down the leg it lies in its up]>er two-thirds upon the 



