The Humerus is the sole bone of the arm.
It is the longest and largest bone of the upper limb.

It articulates proximally with the scapula and distally with both the radius and the ulna.

The proximal end of the humerus(= the head) is shaped like a smooth round ball. Its fits into the glenoid cavity of the scapula. The shape of this shoulder joint allows the arm to hang freely on the side of the body and permits a high degree of flexibility but is not as strong as the hip joint. The head of the humerus is held against the scapula by strong fibrous ligaments connecting the two bones.

The articular surface at the distal end of the humerus is complex. The three fossae (depressions) on either side of the distal end (coronoid, olecranon and radial) accommodate projections on the ulna and radius when the elbow is flexed or extended.
The pulley-shaped trochlea articulates with the ulna and the ball-shaped capitulum articulates with the radius.