THE LOWER LIMB 505 



out into expansions which receive the tendons of the lurabricales 

 and interosseous muscles. In the case of the tendons destined for 

 the second, third, and fourth toes, their expansions are also joined 

 by the outer three tendons of the extensor brevis digitorum. Each 

 tendinous expansion passes forwards over the dorsum of the first 

 phalanx, and at its distal end divides into three 'bands. The 

 middle band is inserted into the dorsal aspect of the base of the 

 second phalanx. The two lateral bands, having united, are inserted 

 into the dorsal aspect of the base of the distal phalanx. 



Nerve-supply. — The anterior tibial nerve. 



Action. — (i) To extend the second and distal phalanges of the 

 four outer toes, and (2) to flex the foot upon the leg. 



Peroneus Tertius--Ong'm. — (i) The anterior surface of the shaft 

 of the fibula in its lower fourth, except for an inch or more below, 

 and (2) the adjacent portion of the anterior surface of the inter- 

 osseous membrane, and the antero-external intermuscular septum 

 between the muscle and the peroneus brevis. 



Insertion. — ^The dorsal surface of the base of the fifth metatarsal 

 bone. 



Nerve-supply. — The anterior tibial nerve. 



Action. — (i) To flex Vie foot upon the leg, and (2) to raise the 

 outer border of the foot slightly. 



The peroneus tertius is to be regarded as a detached portion of 

 the extensor longus digitorum. 



Anterior Tibial Artery. — This vessel is one of the terminal branches 

 of the popliteal artery. It commences at the lower border of the 

 popliteus muscle on a level with the lower border of the tubercle 

 of the tibia (fully ij inches below the level of the upper surface 

 of the head of that bone), and it terminates on the anterior liga- 

 ment of the ankle-joint midway between the two malleoli by 

 becoming the dorsalis pedis artery. Being placed at its commence- 

 ment on the back of the leg, the vessel passes at first forwards 

 between the two heads of the tibialis posticus, and over the upper 

 border of the interosseous membrane, where it lies below the superior 

 tibio-fibular articulation. (The artery sometimes passes through 

 an aperture in the upper part of the interosseous membrane, called 

 the superior hiatus.) Having reached the front of the leg, the 

 vessel changes its course somewhat abruptly, and then descends 

 in close contact with the anterior surface of the interosseous mem- 

 brane, until it reaches the junction of the upper two-thirds and 

 lower third of the leg. Beyond this point it gradually inclines 

 towards the anterior aspect of the tibia, and in the lower fourth it 

 lies upon that surface, and finally upon the anterior ligament of- 

 the ankle-joint. The course of the vessel on the anterior aspect of 

 the leg corresponds with a line drawn from the superior tibio- 

 fibular articulation to the centre of the front of the ankle-joint 

 midway between the two malleoli. 



Relations — On the Back of the Leg. — The artery lies here between 

 the two heads of the tibialis posticus, having the lower border of the 



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