844 HUMAN ANATOMY. 



2. At the middle of the hmb the same interspace is found — usually more 

 easily, as there is often some yellowish-white fatty tissue lying between the muscles 

 and seen as a line on the surface of the deep fascia — and is opened. The artery 

 which still lies on the interosseous membrane will be found in the deeper space thus 

 disclosed between the extensor proprius pollicis and the tibialis anticus. 



3. At the lower third an incision on the same line will expose the vessel lying- 

 usually in the innermost of the two interstices found at that part of the limb, viz., 

 that between the tibialis anticus and the extensor proprius pollicis. Occasionally 

 it will be found to the outer side of the tendon of the extensor proprius — the second 

 tendon from the tibia — in the space between that muscle and the extensor longus 

 digitorum. The vessel lies on the front of the tibia, with the nerve external. 



The collateral circulation is carried on from above the ligature by {a) the pero- 

 neals ; and {b) the posterior tibial, anastomosing respectively with («) the external 

 malleolar, the branches of the dorsalis pedis and the plantar ; and ( b) the internal 

 malleolar from below, assisted by the many small anastomotic vessels piercing the 

 interosseous membrane and derived from the two tibials. 



Branches.— In addition to numerous miiscttlar branches which supply the 

 adjacent muscles, the anterior tibial artery gives ofT the following : 



1. The superior fibular branch (ramus fibularis) is a small vessel which arises 

 from the anterior tibial immediately below its origin ; occasionally it arises by a com- 

 mon trunk with the posterior tibial recurrent or else from the lower part of the 

 popliteal. It passes upward behind the neck of the fibula, traversing the substance 

 of the soleus, and sends branches to that muscle and to the peroneus longus, and 

 anastomoses with the external inferior articular branch of the popliteal. 



2. The posterior recurrent tibial artery (a. recurrens tibialis posterior) arises 

 while the anterior tibial is still upon the posterior surface of the leg. It passes upward 

 between the popliteal muscle and the posterior ligament of the knee-joint, both of 

 which it supplies, and terminates by anastomosing with the external and internal 

 inferior articular branches of the popliteal. 



3. The anterior recurrent tibial artery (a. recurrens tibialis anterior ) is given 

 off just after the anterior tibial has reached the front of the leg. It runs upward in 

 the substance of the tibialis anticus and over the outer tuberosity of the tibia, and 

 terminates by taking part in the formation of the circumpatellar anastomosis. It 

 gives branches to the tibialis anticus, the extensor longus digitorum, the capsule of 

 the knee-joint, and the adjacent integument. This artery is of importance in the 

 establishment of a collateral circulation after ligation of the popliteal artery (page 834), 

 on account of its anastomoses with the descending branch of the external circumflex 

 artery and with the anastomotica magna. 



4. The internal malleolar artery (a. malleolaris anterior medialis) arises from 

 the inner surface of the anterior tibial, a little above the ankle. It passes inward 

 beneath the tibialis anticus, over the surface of the inner malleolus, and terminates 

 by anastomosing with the malleolar branch of the posterior tibial, the internal plantar, 

 and the internal calcaneal arteries. 



5. The external malleolar artery (a. malleolaris anterior lateralis) arises from 

 the outer surface of the anterior tibial, usually a little below the internal malleolar. 

 It is directed outward and downward beneath the extensor longus digitorum and the 

 peroneus tertius, over the surface of the external malleolus, and anastomoses with 

 branches from the anterior and posterior peroneal arteries. 



Anastomoses of the Anterior Tibial Artery. — Collateral circulation is 

 readily established, in cases of interruption of the anterior tibial artery, by means 

 of its abundant anastbmoses with branches of the posterior tibial. Thus there are 

 rich anastomoses between the internal malleolar branch of the anterior tibial and the 

 malleolar branch of the posterior tibial, and between the external malleolar branch of 

 the anterior tibial and the anterior and posterior peroneal branches. Further, since 

 the dorsalis pedis artery is the continuation of the anterior tibial, it will assist mate- 

 rially in the collateral circulation by the anastomoses of its tarsal and metatarsal 

 branches with the plantar and peroneal arteries and by its connections with the 

 plantar arch. 



