216 OSTEOLOGY. 



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 an tero- 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 G'VO-'Z'll. 



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 



