The upper arm contains a single bone, the humerus.
The humerus (fig. 40, A, 1) is a stout, nearly straight, somewhat flattened bone widely expanded at both ends. At the proximal end is the large hemispherical head, which articulates with the glenoid cavity. Behind the head the bone is drawn out into another large rounded process. Below the head the shaft bears a small outgrowth which is continuous with a larger one on the flexor surface (see p. 29). The bone is terminated distally by the trochlea, consisting of three partially distinct convex surfaces which articulate with the bones of the fore-arm.
The fore-arm includes two bones, the radius and ulna; both these are small bones, and are immovably fixed to one another proximally and distally.
The radius or pre-axial bone is the larger of the two, and is a rod-like bone terminated at either end by an epiphysis. It articulates at its proximal end with the humerus, and at its distal end with the radiale or scaphoid bone of the carpus.
The ulna (fig. 40, A, 3) or postaxial bone is shorter than the radius, and more expanded at its proximal end, where it articulates with the humerus. It articulates distally with the intermedium (lunar) and the ulnare (cuneiform) bones of the carpus. All three bones of the arm have their terminations formed by epiphyses which ossify from centres distinct from those forming the shafts.
The Manus consists of the carpus or wrist and the hand which includes the metacarpals and phalanges.
The carpus consists of a series of ten small bones, one of which, the pisiform (fig. 40, A, 10), differs from the others in being merely an ossification in the tendon of a muscle. The remaining nine bones are arranged in a proximal row of three, the ulnare (fig. 40, A, 6), intermedium, and radiale, and a distal row of five (carpalia 1-5), each of which supports one of the metacarpals. A ninth bone, the centrale (fig. 40, A, 7), is wedged in between the two rows. The ulnare, intermedium and pisiform are comparatively large flattened bones, the others are small and cubical.
The hand. This is composed of five digits, each of which consists of a metacarpal and of a varying number of phalanges.
The metacarpals. The first metacarpal (fig. 40, A, 11) is a short flattened bone, the others are all elongated and cylindrical, and are terminated proximally by slightly concave surfaces, and distally by slightly convex ones.
The phalanges. The first and fifth digits both have two phalanges, the second, third, and fourth have each three. The distal phalanx of the first digit is stout and curved, and bears a horny claw; those of the other digits are flattened and more or less pointed.