THE ANTERIOR TIBIAL ARTERY. 585 



The inferior articular arteries, two in number, 'arise from the popliteal beneath 

 the Gastrocnemius, and wind round the head of the tibia below the joint. The 

 internal one first descends along the upper margin of the Popliteus muscle, to which 

 it gives branches ; it then passes below the inner tuberosity, beneath the internal 

 lateral ligament, at the anterior border of which it ascends to the front and inner 

 side of the joint, to supply the head of the tibia and the articulation of the knee, 

 anastomosing with the inferior external articular and superior internal articular 

 arteries. The external one passes outward above the head of the fibula, to the 

 front of the knee-joint, passing in its course beneath the outer head of the Gastroc- 

 nemius, the external lateral ligament, and the tendon of the Biceps muscle, and 

 divides into branches Avhich anastomose with the inferior internal articular artery, 

 the superior external articular artery, and the anterior recurrent branch of the 

 anterior tibial. 



Circumpatellar Anastomosis. Around and above the patella, and on the con- 

 tiguous ends of the femur and tibia, is a large network of vessels, forming a 

 superficial and deep plexus. The superficial plexus is situated between the fascia 

 and skin round about the patella ; the deep plexus, which forms a close network 

 of vessels, lies on the surface of the lower end of the femur and upper end of the 

 tibia around their articular surfaces, and sends numerous offsets into the interior of 

 the joint. The arteries from which this plexus is formed are the two internal and 

 two external articular branches of the popliteal, the anastomotica magna, the 

 terminal branch of the profunda, the descending branch from the external circum- 

 flex, and the anterior recurrent branch of the anterior tibial. 



The Anterior Tibial Artery (Fig. 321). 



The anterior tibial artery commences at the bifurcation of the popliteal at the 

 lower border of the Popliteus muscle, passes forward between the two heads of the 

 Tibialis posticus, and through the large oval aperture above the upper border of 

 the interosseous membrane to the deep part of the front of the leg : it here lies 

 close to the inner side of the neck of the fibula ; it then descends on the anterior 

 surface of the interosseous membrane, gradually approaching the tibia ; and at the 

 lower part of the leg lies on this bone, and then on the anterior ligament of the 

 ankle to the bend of the ankle-joint, where it lies more superficially, and becomes 

 the dorsalis pedis. 



Relations. In the upper two-thirds of its extent it rests upon the interosseous 

 membrane, to which it is connected by delicate fibrous arches thrown across it ; 

 in the lower third, upon the front of the tibia and the anterior ligament of the 

 ankle-joint. In the upper third of its course it lies between the Tibialis anticus 

 and Extensor longus digitorum ; in the middle third, between the Tibialis anticus 

 and Extensor proprius hallucis. At the bend of the ankle it is crossed by the 

 tendon of the Extensor proprius hallucis, and lies between it and the innermost 

 tendon of the Extensor longus digitorum. It is covered, in the upper two-thirds 

 of its course, by the muscles which lie on either side of it and by the deep fascia ; 

 in the lower third, by the integument, anterior annular ligament, and fascia. 



The anterior tibial artery is accompanied by two veins (venae comites), which 

 lie one on each side of the artery ; the anterior tibial nerve, coursing, round the 

 outer side of the neck of the fibula, comes into relation with the outer side of the 

 artery shortly after it has passed through the opening in the interosseous mem- 

 brane ; about the middle of the leg it is placed superficial to it; at the lower part 

 of the artery the nerve is generally again on the outer side. 



