Give the muscular attachments.

The triceps, anconeus, flexor carpi ulnaris, brachialis anticus, pronator teres, flexor sublimis and profundus digitorum, flexor longus pollicis (very often), pronator quadratus, flexor and extensor carpi ulnaris, supinator brevis, extensor ossis metacarpi and longus pollicis, and extensor indicis.

Describe the radius.

Shorter than the ulna, situated upon the outer side of the forearm, with a small upper extremity, forming only a small part of the elbow-joint, its lower end is large, forming the chief part of the wrist-joint. It is slightly curved and of a prismatic form. The head (upper extremity) (Fig. 61) is cylindrical, with a slightly cupped upper surface, articulating with the radial head of the humerus, by its sides with the lesser sigmoid cavity of the ulna and the orbicular ligament by which it is embraced; the constriction beneath the head is the neck; below and to the inner side is the tuberosity, rough toward its posterior margin for the biceps tendon, smooth in front for a bursa; the shaft is prismoid, curved outward, smaller above than below, having a sharp internal interosseous border for the interosseous ligament, with the medullary foramen directed upward at the junction of the middle and upper thirds of the anterior surface. This surface gives attachment to the flexor longus pollicis and pronator quadratus, and by an oblique line to the radial head of the flexor sublimis. The external surface gives attachment to the supinator brevis and pronator teres. The posterior surface (Fig. 62) gives attachment to the supinator brevis, extensor ossis metacarpi pollicis, and extensor brevis pollicis.

The lower carpal extremity has on its lower face an articular surface divided by a slight ridge into two facets for the semilunar and scaphoid bones; upon its inner side the shallow sigmoid cavity for the ulnar head; externally the styloid process giving attachment by its apex to the external lateral ligament, by its base to the supinator longus muscle; and on its posterior and external convex surfaces are five grooves for the extensor tendons.

How is this bone developed ?

By three centers: one for the shaft (eighth fetal week):

FIG. 62.-Bones of the left forearm, posterior surface.

one for the carpal extremity (second year); and one for the head (fifth year, joins the shaft at puberty); bone coössified by about the twentieth year.

Give the muscular attachments.

The biceps, the supinator brevis, flexor digitorum sublimis and longus pollicis, pronator quadratus, the extensor ossis metacarpi and brevis pollicis, pronator teres, and supinator longus.

The Hand.

Into what segments is the hand divided?

Into the carpus (eight bones), metacarpus (five bones), and phalanges (fourteen bones); total, twenty-seven bones.

Describe the arrangement of the carpal bones.

They are placed in two rows of four each; thus, enumerating from the radial to the ulnar side, with palm upward; first,

or proximal row: scaphoid, semilunar1, cuneiform, pisiform P; second, or distal row: trapezium*, trapezoid', ', os magnum, unciform ".

With how many bones does each articulate?

Scaphoid, five; semilunar, five; cuneiform, three; pisiform, one; trapezium, four; trapezoid, four; os magnum, seven; unciform, five.

Describe the chief peculiarities of each bone (Figs. 63, 64, and 65).

The scaphoid (boat-shaped) has on the anterior surface a tuberosity; a transverse groove on the dorsum parallel to the convex articular surface for the radius; facets for the os magnum and semilunar bones on its inner surface; on its lower surface are facets for the trapezium and trapezoid.

The semilunar (half-moon) presents a convex facet above for the radius and a part of the triangular fibro-cartilage; on

FIG. 64.-Bones of the left hand, dorsal surface (Gray).

its outer face a semilunar facet for the scaphoid; on its lower, a concave one for the os magnum and apex of the unciform; a quadrilateral one on the inner face for the cuneiform.

The cuneiform (wedge-shaped) has an oval facet in front for

the pisiform; one external for the semilunar; an inferior concavo-convex facet for the unciform; a superior convex facet for the triangular fibro-cartilage.

The pisiform is rounded, with one ovoidal facet for the cuneiform.

The trapezium is obliquely grooved on its palmar surface for the tendon of the flexor carpi radialis; superiorly is a concave facet for the scaphoid; below, a saddle-shaped one for the first metacarpal; internally, one large concave facet for the trapezoid, and a smaller one for the second metacarpal.

The trapezoid1t is wedge-shaped, apex palmar, has four articular surfaces touching, separated by sharp edges, the external for the trapezium; inferior (like a ridge-roof), for the second metacarpal; internal, for the os magnum; superior, for the scaphoid.

The os magnum' has superiorly a convex head for the scaphoid and semilunar, a neck and body; below, facets for three metacarpal bones; externally, one for the trapezoid; internally, one for the unciform.

The unciform" is triangular, has a sigmoid internal articular facet for the cuneiform; two facets below for the fourth and fifth metacarpals; one, external, for the os magnum; by apex with the semilunar; from the palmar surface projects the curved unciform process.

When do these bones ossify?

Os magnum and unciform, during the first year; cuneiform, third year; trapezium and semilunar, fifth year; scaphoid, sixth year; trapezoid, during the eighth year; pisiform, about the twelfth year.

(The muscular attachments to the carpal and tarsal bones will be given under the Muscular System.)

Describe the metacarpal bones.

They are five long bones, with shaft, head, and base. The first metacarpal (sometimes considered a phalanx) is shorter, has only one facet on the base, and has one ossific center for the shaft (eighth fetal week) and one for the base (third year). The second metacarpal has four facets on the base for the trapezium, trapezoid, os magnum, and third metacarpal; it, in common with the rest, has one ossific center for the shaft