The os humeri in man is an elongated cylindrical bone, surmounted superiorly by a convex head, directed obliquely upwards, inwards, and backwards, and separated from the shaft by a constricted neck. At the junction of the neck and the shaft are two tuberosities, between which is a groove, which receives the tendon of the biceps flexor cubiti muscle. The greater tuberosity, external and posterior, receives the insertions of the supra-spinatus, the infraspinatus, and the teres minor muscles, upon distinct facettes of bone; the lesser tuberosity, placed internal and anterior, affords attachment to the tendon of the subscapularis.
Two prominent ridges, leading from the tuberosities to the shaft of the bone, upon which they are lost, mark the bicipital groove, and give attachment to muscles; on the anterior ridge is inserted the tendon of the pectoralis major; on the posterior those of the latissimus dorsi and the teres major. The outer surface of the bone, a little above its centre, is marked by a rough surface for the attachment of the deltoid muscle.
The bone becomes flattened and expanded laterally at its distal extremity, where two prominent lines lead to eminences situated upon its radial and ulnar side. The eminence upon the radial side (epicon-dyle) surmounts a convex surface of bone, the condyle, upon which rotates the cup-shaped head of the radius: the eminence upon the ulnar side (epitro-chlea), larger and more prominent than the epicondyle, surmounts a pulley-like convex surface, the trochlea, which receives the articulating extremity of the ulna, and terminates in two fossae, one anterior, to receive the coronoid process when the arm is flexed; one posterior, for the olecranon in extension. The os humeri, when viewed in its totality, appears twisted upon itself; the flat distal extremity being curved forwards, whilst the inwardly directed head maintains its normal connection with the shaft. The hand, therefore, is supine instead of prone, as is the case with the foot; the pronator radii teres muscle is said to arise from the inner and not from the outer condyle, as does its homotype in the leg, the popliteus, etc.