The Common Interosseal Artery comes off immediately below the recurrents, and descends backwards and outwards to the superior margin of the interosseous ligament, where it divides into the anterior and posterior interosseal arteries. Before its division it gives off a small but pretty constant artery, the comes nervi mediani, which accompanies the median nerve to the wrist, where it terminates: occasionally this artery is of considerable size, and joins the superficial palmar arch: it is sometimes a branch of the ulnar. The Anterior interosseal artery descends on the front of the interosseous ligament, between the flexor pollicis longus and flexor digitorum profundus muscles, being covered and accompanied down the fore-arm by a branch of the median nerve; in its course down the fore-arm it sends small branches to the muscles in relation to it, and two or three very small perforating arteries which pass through the interosseous ligament and supply the deep-seated muscles on the back of the fore-arm. Having arrived at the pronator quadratus muscle, the anterior interosseal divides into two branches: one supplies this muscle, and terminates in anastomosing with the carpal arteries and the deep palmar arch; the other passes backwards through an oval opening in the lower portion of the interosseous ligament, to anastomose with the posterior carpal and posterior interosseal arteries. The Posterior interosseal artery passes downwards and backwards, between the anterior oblique and interosseous ligaments, and, having thus arrived at the posterior superior part of the fore-arm, gives off the interosseal recurrent branch, improperly called the "posterior radial recurrent artery," which ascends between the supinator brevis and anconeus muscles, and then through the fossa between the external condyle of the humerus and the olecranon process: after piercing the triceps muscle it terminates in anastomosing with the superior profunda and posterior ulnar recurrent arteries. After giving off this recurrent branch, the posterior interosseal artery descends on the back of the fore-arm, not lying on the interosseous ligament, but placed between the superficial and deep layer of muscles. In this course it is accompanied by a branch of the musculo-spiral nerve, and gives off numerous branches to the surrounding muscles ; at the wrist the artery becomes very small, and terminates in anastomosing with the anterior interosseal and the posterior carpal arteries.

The Muscular Branches

The Muscular Branches pass off from the ulnar artery in its course along the fore-arm, and supply the various muscles with which it is related.

The Anterior Carpal Branch

The Anterior Carpal Branch, extremely small, passes horizontally outwards, along the inferior margin of the pronator quadratus muscle, and behind the tendons of the superficial and deep flexors. It anastomoses with the anterior carpal branch of the radial artery.