A, Anatomy of interosseous arteries. Common interosseous artery (1) divides into anterior interosseous artery (2), running volar to interosseous membrane, and posterior interosseous artery (3). Distally, anterior interosseous artery approaches posterior compartment of forearm (2) and gives branches to dorsal aspect of wrist and forearm that anastomose with cutaneous branches of posterior interosseous artery (4). Area of skin on dorsal aspect of forearm irrigated by posterior interosseous artery (5). B, Transverse section at middle third of forearm where posterior interosseous artery runs immediately beneath superficial fascia of dorsal aspect of forearm. 1, Anterior interosseous artery; 2, extensor carpi ulnaris muscle; 3, extensor digiti minimi muscle; 4, posterior interosseous artery between muscles 2 and 3, with some branches perforating superficial fascia to reach skin; 5, posterior interosseous nerve. R, Radius; U, ulna.