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The supinator muscle is seen in both the flexor compartment and extensor compartment of the forearm. The fibers of the supinator muscle wrap laterally around the upper one-third of the radius.
To view the supinator muscle, supinate the forearm and retract the extensor muscles that form the lateral border of the cubital fossa. Deep in the cubital fossa, identify the supinator muscle and radial nerve.In the proximal portion of the cubital fossa, the radial nerve divides into its superficial and deep branches [the deep branch lies superficial to the tip of the probe and the superficial branch lies beneath the curve of the probe]. Trace the superficial branch of the radial nerve distally and identify its branches which supply the skin of the dorsum of the hand over the thumb, index and middle fingers.
Links and References:
Grant's: 6.83 and 6.116
Netter (1ed.): 451 and 453 (2ed.): 447 and 449
Rohen/Yokochi: 392, 397, and 398