The human humerus is a long tubular bone of the upper limb (arm). It consists of a shaft and two ends, which are called epiphysis. The upper portion of the shaft is round, while the lower part is trihedral.
The posterior surface of the shaft of humerus features the spiral groove, which lodges the radial nerve. It runs downwards and laterally. Meanwhile, the anterior surface is divided by a poorly defined border into an anteromedial surface and an anterolateral surface, which is the site of origin of the brachialis muscle. The lower half of the anteromedial surface has a nutrient foramen, which leads into a distally running nutrient canal. The deltoid tuberosity is lacated on the anterolateral surface of this bone.
The proximal epiphysis, which is the upper end, is thickened and it features the semispherical head of humerus. The head articulates with the glenoid cavity of scapula and it is separated from the rest of the bone by a shallow annular constriction, which is the anatomical neck.
The greater tuberosity and the lesser tuberosity are located right below the anatomical neck, on the anterolateral surface. They are separated from one another by the intertubercular groove. The greater tuberosity provides attachment to the supraspinatus, infraspinatus, and teres minor muscle, while the lesser tuberosity is the site of attachment for the subscapularis muscle.
The distal epiphysis, or lower end, is flattened in the anteroposterior direction. The distal segment of this bone bears in its lateral part a rounded eminence called the capitulum of the humerus, which is for articulation with the head of the radius bone. The trochlea of humerus is found next to this eminence, which is for articulation with trochlear notch of the ulna.
The distal epiphysis ends up in the lateral and medial epicondyle. The medial epicondyle is larger, with its posterior surface bearing the groove of the ulnar nerve. This groove and the epicondyles are easily palpated (felt with the tips of fingers) under the skin.
Below, the anterior and posterior view of the human humerus (right arm).
