How do you tell a right humerus from a left humerus?
You look for the side where the capitulum is located.
First, you must be able to recognize a humerus.
The humerus is the long bone in the arm that runs from the shoulder to the elbow.
The upper end has a rounded head.
The lower end has two processes (projections) in the front.
One is the trochlea (Latin for pulley, referring to the groove in a pulley).
The other is the capitulum (little head).
A distinguishing characteristic in the posterior view is the olecranon fossa (head of elbow trench).
Right or left?
Orient the bones so that the rounded head is up.
Look for the deep olecranon fossa on the lower (distal) end.
Rotate the humerus so that the capitulum and trochlea face YOU.
If the capitulum is on the left side of the bone, it is a left humerus. If the capitulum is on the right side, it is a right humerus.
Just to make it clear, the rotating image at the top of this page represents a left humerus and the image below it is of a right humerus.