TE-9 Sidu (四瀆) — Four Rivers

On the dorsal aspect of the forearm, 5 cun distal to the olecranon, between the radius and the ulna.

With the arm extended and pronated, locate the point 7 cun above the dorsal wrist crease, or 5 cun distal to the olecranon, between the ulna and the radius.

Extensor digitorum communis and extensor carpi ulnaris muscles. Innervated by the posterior antebrachial cutaneous nerve and the posterior interosseous nerve.

Perpendicular insertion, 0.5–1.0 cun.

Si (四), four; Du (瀆), river. The Yangtze, Yellow, Huai He, and Ji Shui rivers were called Si Du in ancient times. The point lies between the radius and the ulna, as if it were a river.