humerus

Humerus is the Latin word for the upper arm bone — the single long bone between the shoulder and the elbow. The word comes from Latin umerus or humerus (shoulder, upper arm), which is related to Greek ōmos (shoulder). The Romans used humerus for both the shoulder region and the bone within it. The anatomical narrowing — from 'shoulder area' to 'specific bone' — happened gradually as medical Latin became more precise.

The humerus is the third-largest bone in the body, after the femur and tibia. Its upper end forms a ball-and-socket joint with the scapula (the shoulder), and its lower end forms a hinge joint with the ulna and radius (the elbow). The humerus is where the body's most mobile joint (the shoulder) meets one of its most stable joints (the elbow). The bone is a transition between freedom and constraint.

The 'funny bone' pun is irresistible and inaccurate. Hitting your 'funny bone' — the sharp, tingling pain that radiates from the elbow — is caused by striking the ulnar nerve, which runs through a groove (the cubital tunnel) behind the medial epicondyle of the humerus. The nerve is exposed and unprotected at this point. The pain is the nerve's, not the bone's. But humerus sounds like humorous, and the pun has survived for at least two centuries.

English uses both 'humerus' (Latin, medical) and 'upper arm bone' (English, descriptive). The Latin term won in anatomy textbooks. The funny bone joke won in conversation. The bone exists in both worlds, medical and comedic, because of a coincidence of spelling that Latin did not intend and English cannot resist.