Click image to view full screen
Note that it crosses the elbow joint but does not cross the wrist.
Next, retract the brachioradialis muscle laterally and identify the superficial branch of the radial nerve [probe; forceps hold thebrachioradialis muscle]. Trace the superficial branch of the radial nerve proximally to identify its origin from the radial nerve.
Links and References:
Grant's: 6.78 and 6.80
Netter (1ed.): 420 and 421 (2ed.): 416 and 417
Rohen/Yokochi: 366 and 393-397