Bony landmark · Shoulders

Glenoid fossa

Cavitas glenoidalis

The glenoid fossa is the socket of the shoulder: a shallow, pear-shaped dish on the outer angle of the shoulder blade that the head of the arm bone rests against. It is far smaller and flatter than the ball it holds — the anatomical reason the shoulder trades stability for range, and the reason the rotator cuff has to work constantly to keep the head centred on it. A rim of cartilage, the labrum, deepens it slightly. The long head of the biceps arises from a tubercle just above it and the long head of the triceps from a tubercle just below.