838 HUMAN ANATOMY. 



divided in the line of the skin wound, the inner margin of the soleus displaced 

 outward, and the vessel, with its vence comites, exposed, the posterior tibial nerve 

 lying to its outer side. A little lower — i.e., in the lower third of the leg — the 

 incision should be made midway between the inner edge of the tibia and the inner 

 edge of the tendo Achillis, and the artery will be found lying on the fibres of the 

 flexor Ibngus digitorum, the tendon to the inner side, and the nerve external. 



3. To ligate the vessel at the inside of the ankle the incision should be semi- 

 lunar in shape, parallel with the margin of the inner malleolus, and about half-way 

 between it and the margin of the tendo Achillis. After dividing the deep fascia — 

 internal annular ligament — the artery will be found, with its accompanying veins, 

 lying between the flexor longus digitorum and tibialis posticus tendons on the inside 

 — each in a separate synovial sheath and the latter near the malleolus — and the 

 nerve and flexor longus pollicis tendon on the outside. The sheaths of these tendons 

 should not be opened. 



The collateral circulation is carried on from abo\'e the ligature by («) the 

 anterior and posterior peroneal arteries and their muscular and communicating 

 branches; ((5) the external malleolar branch of the anterior tibial; (r) the internal 

 malleolar (anterior tibial); (af) the dorsalis pedis. Anastomosing respectively 

 with («) the muscular branches and the communicating branch of the posterior 

 tibial ; (<^) the external plantar branch of the posterior tibial ; {c) the internal malle- 

 olar (posterior tibial) ; and (t/) the internal and external plantars, 



1. The Nutrient Artery. — The nutrient artery to the tibia (a. nutritia tibiae) 



may arise from the posterior tibial, either above or below the origin of the peroneal 

 artery, or sometimes it arises from that vessel. It pierces the tibialis posticus and 

 enters the nutrient foramen on the posterior surface of the tibia, sending off, before 

 it does so, some small muscular branches. 



2. The Peroneal Artery. — The peroneal artery (a. peronaea) (Fig. 736) is by 

 far the largest of the collateral branches of the posterior tibial. It arises about 2.5 cm. 

 below the lower border of the popliteus muscle and is at first directed outward and 

 downward towards the fibula, and then passes vertically downward along the inner 

 surface of that bone to a point about 2.5 cm. above the ankle-joint, where it termi- 

 nates by dividing into the anterior and posterior peroneal arteries. 



Relations. — In the upper part of its course it is covered posteriorly by the 

 soleus, lying between that muscle and the tibialis posticus. Lower down it passes 

 beneath the flexor longus hallucis or else traverses the substance of that muscle, and 

 just before its termination it emerges from beneath the muscle and becomes super- 

 ficial. It is accompanied by two venae comites. 



Branches. — In addition to numerous muscular branches to the neighboring muscles and 

 cutaneous branches to the integument of the outer border of the crus, the peroneal artery gives 

 off the following vessels : 



(a) The nutrient artery to the fibula (a. nutritiae fibulae) enters the nutrient foramen of that 

 bone. 



{b) The communicating branch (ramus communicans) passes inward over the lower end of 

 the tibia and beneath the tendo Achillis, a short distance above the terminal bifurcation of the 

 peroneal. It inosculates with the communicating branch of the posterior tibial. 



{c) The anterior peroneal artery (ramus perforans) is one of the terminal branches of the 

 peroneal. It passes directly forward and, perforating the interosseous membrane, bends down- 

 ward over the ankle-joint to the dorsum of the foot. It sends branches to the ankle-joint and 

 to the inferior tibio-fibular articulation, as well as to the peroneus tertius muscle, beneath which 

 it passes, and terminates by anastomosing with the tarsal and metatarsal branches of the dorsalis 

 pedis and with the external plantar artery upon the side of the foot. 



{d) The posterior peroneal artery is the other terminal branch of the peroneal, of which 

 it is the direct continuation. It gives origin to the external calcaneal branch which ramifies 

 over the outer surface of the os calcis and terminates by anastomosing with the internal cal- 

 caneal branch of the posterior tibia^ artery and with the tarsal and metatarsal branches of the 

 dorsalis pedis. 



Variations. — The peroneal artery is exceedingly subject to variation. It is rarely absent, 

 but not infrequently it terminates over the outer malleolus, its lower portion being given off from 

 a branch which passes across from the posterior tibial and represents the enlarged anastomosis 



