(a) Humerus (Figure 20.16). (1) This is a long and strong bone of the upper arm which articulates with the glenoid cavity of the pectoral girdle at the proximal end and with the radius-ulna at the distal end. (2) The humerus consists of a rounded head, neck, greater and lesser tuberosities and inner tubercular sulcus at the upper end. Various muscles are attached on the tuberosities and the sulcus. (3) The shaft is long, with nutrient foramen, tuberosities and a groove for the radial nerve. (4) The lower end consists of the capitulum, which articulates with head of radius, and the trochlea, which is pulley-shaped and articulates with the trochlear notch of the ulna. (5) The lower his end also shows a blunt medial epicondyle, lateral epicondyle,and coronoid and radial fossae. Fracture of the shaft at the lower end may damage radial and ulnar nerves.