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which rolls within the radial notch of the ulna in the movements of pronation and supination. The character of the lateral half of the circumference differs from the medial, in being narrower, and rounded proximo-distally.
The collum radii (neck) is the constricted part of the body which supports the head, the overhang of the latter being greatest towards the lateral and dorsal side. Distal to the neck, on the medial side, there is an outstanding oval prominence, the tuberositas radii (radial tuberosity). The dorsal part of this is rough for the insertion of the biceps tendon, whilst the volar half is smooth and covered by a bursa which intervenes between it and the tendon.
EXTENSOR DIGITORUM COMMUNSI
The body (corpus radii), which has a lateral curve and is narrow proximally and broad distally, is wedge-shaped on section. The edge of the wedge forms the sharp medial interosseous crest of the bone (crista interossea), whilst its base corresponds to the thick and rounded lateral border over which the volar or anterior surface becomes confluent with the dorsal or posterior surface.
The interosseous crest, faint proximally where it lies in line with the dorsal margin of the tuberosity, becomes sharp and prominent in the middle third of the bone. Distal to this it splits into two faint lines, which lead to either side of the ulnar notch on the distal end of the bone, thus including between them a narrow triangular area into which the deeper fibres of the pronator quadratus muscle are inserted. To this crest, as well as to the dorsal of the two divergent lines, the interosseous inembrane is attached.
The lateral surface (once described as the lateral border) is thick and rounded proximally, but becomes thinner and more prominent distally, where it merges with the base of the styloid process. About its middle the anterior and posterior oblique lines become confluent with it, and here, placed between them, is a rough elongated impression which marks the insertion of the pronator teres muscle. Proximal to this, and on the lateral surface of the neck, the supinator muscle is inserted, whilst distally this surface is overlain by the tendons of the brachio-radialis and the extensor carpi radialis longus and brevis muscles.
EXTENSOR POLLICIS LONGUS
FIG. 207.-DORSAL ASPECT OF BONES OF RIGHT FORE
ARM WITH ATTACHMENTS OF MUSCLES MAPPED OUT.
The volar or anterior surface (facies volaris) is crossed obliquely by a line which runs from the tuberosity distally and laterally towards the middle of the lateral surface of the body. This, often called the anterior oblique line, serves for the attachment of the radial head of origin of the flexor digitorum sublimis muscle. Proximal to it, the volar aspect of the bone has the fibres of the supinator muscle inserted into it, whilst distal and medial to it, extending as far as the distal limit of the middle third of the bone, is an extensive surface for the origin of the flexor pollicis longus muscle. In the distal fourth of the bone, where the volar aspect of the body is broad and flat, there is a surface for the insertion of the pronator quadratus muscle, which also extends dorsally to the interosseous ridge. The dorsal or posterior surface (facies dorsalis) is also crossed by an oblique line, less distinct than the anterior. This serves to define the proximal
limit of the origin of the abductor pollicis longus muscle. Proximal to this, the dorsal aspect of the neck and proximal part of the body is overlain by the fibres of the supinator muscle which become attached to this surface of the bone in its lateral half. Distal to the posterior oblique line the dorsal surface in the proximal part of its medial half gives origin to the abductor pollicis longus and the extensor pollicis brevis muscles, in that order proximo-distally.
The distal extremity, which tends to be turned slightly forwards, has a somewhat triangular form. Its distal carpal articular surface, concave from before backwards, and slightly so from side to side, is divided into two facets by a slight antero-posterior ridge, best marked at its extremities where the volar and dorsal margins are notched; the lateral of these areas, of triangular shape, is for articulation with the navicular, whilst the medial, quadrilateral in form, is for the os lunatum. The volar border, prominent and turned forwards, is rough at its edge, where it serves for the attachment of the volar part of the capsule of the wrist-joint. The dorsal border is rough, rounded, and tubercular, and is grooved by many tendons; of these grooves the best marked is one which passes obliquely across its dorsal surface. This is for the tendon of the extensor pollicis longus muscle. The lateral lip of this groove is often very prominent, and forms an outstanding tubercle. To the medial side of this oblique groove there is a broad shallow furrow in which the tendons of the extensor digitorum communis and extensor indicis proprius muscles are lodged, whilst to its lateral side, and between it and the styloid process, there is another broad groove, subdivided by a faint ridge into two, for the passage of the tendons of the extensor carpi radialis brevis medially and the extensor carpi radialis longus laterally. The styloid process lies to the lateral side of the distal extremity; broad at its base, it becomes narrow and pointed distally where by its medial cartilage-covered surface it forms the summit of the distal triangular articular area. The lateral surface of this process is crossed obliquely distally and forwards by a shallow groove, the volar lip of which is sharp and well marked, and serves to separate it from the volar surface of the bone, whilst the dorsal lip is often emphasised by a small tubercle above. The tendon of the brachio-radialis muscle is inserted into the proximal parts of both lips, and also spreads out on to the floor of the groove, whilst the tendons of the abductor pollicis longus and the extensor pollicis brevis muscles lie within the groove. To the tip of the styloid process is attached the radial collateral ligament of the wrist. On the medial side of the distal extremity is placed the incisura ulnaris (ulnar notch) for the reception of the head of the ulna. Concave from before backwards, and plane proximo-distally, it forms by its inferior margin a rectangular edge which separates it from the distal carpal surface. To this edge the base of the articular disc is attached, a structure which serves to separate the distal articular surface of the head of the ulna from the carpus. The volar and dorsal edges of the ulnar notch, more or less prominent, serve for the attachment of ligaments.
The proportionate length of the radius to the body height is as 1 is to 6.70-7.11. Nutrient Foramina.-The openings of several small nutrient canals may be seen in the region of the neck. That for the body, which has a proximal direction, is usually placed on the volar surface of the bone, medial to the anterior oblique line, and from an inch and a half to two inches distal to the tuberosity. The dorsal surface of the distal extremity of the bone is pierced by many small vascular foramina.
Connexions.-The radius articulates with the capitulum of the humerus in the flexed position of the elbow, with the ulna to its medial side by the proximal and distal radio-ulnar joints, and with the navicular and lunate bones of the carpus distally. Proximally, the head of the bone can be felt in the intermuscular depression on the lateral side of the back of the elbow; here the bone is only covered by the skin, superficial fascia, and the thin common tendinous origin of the extensor muscles, as well as the ligaments which support it. Its position can best be ascer tained by pronating and supinating the bones of the forearm, when the head will be felt rotating beneath the finger. The distal end of the bone is overlain on the volar and dorsal aspects by the flexor and extensor tendons, but its general form can be readily made out. The styloid process lying to the lateral side of the wrist in line with the extended thumb can easily be recognised note that it reaches a more distal level than the corresponding process of the ulna. The lateral border of the lower third of the body can be distinctly felt, as here the bone is only overlain by tendons.
Ossification. The centre for the body makes its appearance early in the second
Fuses with shaft 18-20 years body is well formed; its proximal and distal extremities are capped with cartilage, and the tuberosity is beginning to appear. A secondary centre appears in the cartilage of the distal extremity about the second or third year; this does not unite with the body until the twentieth or twenty-fifth year, somewhat earlier in the female. From this the carpal and ulnar articular surfaces are formed. The centre for the head appears from the fifth to the seventh year, and fuses with the neck about the age of eighteen or twenty. It forms the capitular articular surface and combines with the neck to form the area for articulation with the radial notch of the ulna. A scale-like
FIG. 209.-THE BONES OF THE RIGHT WRIST AND HAND
os hamatum (O.T. unciform). Irregularly six-sided, each of these bones possesses non-articular volar and dorsal surfaces. In addition, the marginal bones are nonarticular along their ulnar and radial aspects according as they form the medial or lateral members of the series.
Os Naviculare (O.T. Scaphoid).-The navicular is the largest and the most lateral
ABDUCTOR POLLICIS BREVIS
ABDUCTOR POLLICIS LONGUS
FLEXOR CARPI RADIALIS
POLLICIS TRANSVERSE HEAD
ABDUCTOR DIGITI QUINTI
FLEXOR CARPI ULNARIS
bone of the first row. Its volar surface, rough for the attachment of ligaments, is irregularly triangular. The distal angle on the lateral side forms a projection called the tuberosity; this can be felt at the base of the root of the thumb. Its proximal surface is convex from side to side and before backwards for articulation with the radius. This area extends considerably over the dorsal surface of the bone. Its distal surface is convex from before backwards, and extends on to the dorsal aspect of the bone, slightly convex from side to side; it is divisible into two areas, the lateral for articulation with the greater multangular, the medial for the lesser multangular. The lateral surface is narrow and rounded and forms a non-articular border, which extends from the radial articular surface proximally to the tuberosity distally. The medial surface is hollowed out in front for articulation with the head of the capitate bone. Proximal to this it displays a small semilunarshaped facet for the os lunatum. The dorsal non-articular surface lies between the lateral articular surface proxi
FIG. 210.-VOLAR ASPECT OF BONES OF THE RIGHT CARPUS
mally and the surface for EXTENSOR CARPI the greater and lesser multangular bones distally. It is obliquely grooved for the attachment of the dorsal ligaments of the wrist. The navicular articulates with five bones - the radius, the os lunatum, the capitate, the lesser multangular, and the greater multangular.
EXTENSOR CARPI RADIALIS BREVIS
EXTENSOR CARPI RADIALIS LONGUS
Os Lunatum (O.T. Semilunar Bone).- So called from its deeply excavated form, the os lunatum lies between the navicular on the lateral side and the os triquetrum on the medial. Its volar surface, of rhombic form and considerable size, is rough for the attachment of ligaments; its proximal surface, convex from side to side and from before backwards, articulates with the radius and in part with the distal surface of the articular disc of the wrist. Its distal aspect, deeply
FIG. 211.-DORSAL ASPECT OF BONES OF THE RIGHT CARPUS AND
hollowed from before backwards, is divided into two articular areas, of which the lateral is the larger; this is for the head of the capitate bone; the medial, narrow from side to side, articulates with the os hamatum. Its lateral surface, crescentic in shape, serves for articulation with the navicular, and also for the attachment of the interosseous ligaments which connect it with that bone. Its medial surface, of quadrilateral form, is cartilage-covered for articulation with the os triquetrum, and the edge which separates this from the proximal surface has attached to it the interosseous ligament which unites these two bones. The rough dorsal non-articular surface is much smaller than the volar; by this means the volar and dorsal surfaces of the bone can readily be determined. The os lunatum articulates with five bones-the navicular, the radius, the os triquetrum, the os hamatum, and the capitate bone.
Os Triquetrum (O.T. Cunei
form). This bone may be recognised by the small oval or circular facet on its volar surface for the pisiform. This is placed towards the distal part of the volar surface, which is elsewhere rough for ligaments. The bone is placed obliquely, so that its surfaces. cannot be accurately described as distal, proximal, etc.; but for convenience of description, the method already adopted is adhered to. The proximal surface has a convex rhombic area for articulation with the distal surface of the articular disc in adduction of the hand, though ordinarily it does not appear to be in contact with that structure. To the medial side of this it is rough for ligaments. The distal surface is elongated and concavo-convex from radial to ulnar side; here the bone articulates with the os hamatum. The lateral surface, broader in front than behind, articulates with the os lunatum. The medial surface, rounded and rough, is confluent proximally and dorsally with the proximal
FIG. 212. THE BONES OF THE RIGHT WRIST AND HAND
and dorsal aspects of the bone. The dorsal surface, rounded and smooth laterally, is ridged and grooved medially for the attachment of ligaments. The os triquetrum articulates with three bones, viz., the pisiform, the os hamatum, and the os lunatum. Os Pisiforme.-About the size and shape of a large pea, the pisiform bone rests on the volar surface of the os triquetrum, with which it articulates by an oval or circular facet on its dorsal aspect. The rounded mass of the rest of the bone is non-articular, and inclines distally and laterally so as to overhang the articular facet in front and laterally. The mass of the bone is usually separated from the articular surface by a small but distinct groove. Into the summit of the bone the tendon of the flexor carpi ulnaris muscle is inserted, and