The head of the radius can be felt to rotate in the dimple on the back of the elbow just below the lateral epicondyle.
"Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition." by Alexander Miles
On the lateral parts of this extremity we find: internally, a prominence, the epitrochlea; and, externally, another, the epicondyle.
"Artistic Anatomy of Animals" by Édouard Cuyer