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Other Terms: Humérus, Húmero
The humerus is the largest bone of the upper limb. It has a long cylindrical shaft with expanded ends. The proximal end is rounded, while the distal end is ventrodorsally flattened. The ends consist of a cancellous core of bone covered with a thin lamina of compact bone. The shaft is a cylinder of thick compact bone surrounding a large medullary cavity. It sits between the shoulder and elbow.
The Latin term humerus is closely related to the Greek omos meaning shoulder. It later came to refer to the large bone of the upper limb or arm bone.
The humerus articulates with three bones: the scapula, ulna, and radius. At its proximal end the round, ball-like head articulates with the glenoid cavity of the scapula. At the distal end of the bone exist two articular surfaces, one lateral and one medial. The lateral surface, a small dome-like projection called the capitulum, articulates with the head of the radius. The medial surface forms a pulley-like wheel, the trochlea, which articulates with the trochlear notch of the ulna.
The humerus ossifies endochondrally from eight centers. The first center appears during the eighth fetal week as an artery penetrates the diaphysis of the cartilage anlage or model. This establishes the primary center for the shaft of the femur. By birth ossification of the diaphysis is complete. Seven additional centers of ossification appear after birth. During the first year an ossification center appears in the head. This is followed by the greater tubercle center during the third year and the lesser tubercle center during the fifth year. By the sixth year these three epiphyseal centers have fused and cap the shaft with a growth plate. This growth plate remains until the twentieth year when fusion occurs. At the distal end a secondary center of ossification emerges in the capitulum during the first year quickly establishing the articular surface. In the fourth year a center for the medial epicondyle arises. During the tenth year a center appears for the trochlea. The final center arises in the lateral epicondyle during the twelfth year. All these centers, except the medial epicondyle, converge at puberty and the consolidated epiphysis fuses with the shaft around the fifteenth year. The medial epicondyle remains as a separate extracapsular epiphysis fusing during the twentieth year.