THE RADIUS. 



157 



Appears at 

 5th year. 



Head. 



Appears at_j^ 

 2d year. 



with shaft 

 about puberty. 



shallow, and subdivided into two by a slightly elevated ridge: the outer of these 

 two transmits the tendon of the Extensor carpi radialis longior, the inner the 

 tendon of the Extensor carpi radialis brevior. The second, which is near the 

 centre of the bone, is a deep but narrow groove, bounded on its outer side by a 

 sharply-defined ridge ; it is directed obliquely from above, downward and outward, 

 and transmits the tendon of the Extensor longus pollicis. The third, lying most 

 infernally, is a broad groove, for the passage of the tendons of the Extensor indicis 

 and Extensor communis digitorum. 



Structure. Similar to that of the other long bones. 



Development (Fig. 103). By three centres: one for the shaft and one for each 

 extremity. That for the shaft makes its appearance near the centre of the bone, 

 about the eighth week of foetal life. About the end of the second year ossifi- 

 cation commences in the lower epiphysis, and 

 about the fifth year in the upper end. At the 

 age of seventeen or eighteen the upper epiphysis 

 becomes joined to the shaft, the lower epiphysis 

 becoming united about the twentieth year. 



Articulation. With four bones : the humerus, 

 ulna, scaphoid, and semilunar. 



Attachment of Muscles. To nine : to the 

 tuberosity, the Biceps ; to the oblique ridge, 

 the Supinator brevis, Flexor sublimis digitorum, 

 and Flexor longus pollicis ; to the shaft (its 

 anterior surface), the Flexor longus pollicis and 

 Pronator quadratus ; (its posterior surface), the 

 Extensor ossis metacarpi pollicis and Extensor 

 brevis pollicis ; (its outer surface), the Pronator 

 radii teres ; and to the styloid process, the 

 Supinator longus. 



Surface Form. Just below and a little in front of 

 the posterior surface of the external condyle a part of 

 the head of the radius may be felt, covered by the orbic- 

 ular and external lateral ligaments. There is in this situ- 

 ation a little dimple in the skin, which is most visible 

 when the arm is extended, and which marks the posi- 

 tion of the head of the bone. If the finger is placed on 

 this dimple and the forearm pronated and supinated, 

 the head of the bone will be distinctly perceived rotating 

 in the lesser sigmoid cavity. The upper half of the 

 shaft of the radius cannot be felt, as it is surrounded by 



the fleshy bellies of the muscles arising from the external condyle. The lower half of the shaft 

 can be readily examined, though covered by tendons and muscles and not strictly subcutaneous. 

 If traced downward, the shaft will be felt to terminate in a lozenge-shaped, convex surface on 

 the outer side of the base of the styloid process. This is the only subcutaneous part of the bone, 

 and from its lower extremity the apex of the styloid process will be felt bending inward toward 

 the wrist. About the middle of the posterior aspect of the lower extremity of the bone is a 

 well-marked ridge, best perceived when the hand is slightly flexed on the wrist. It forms the 

 outer boundary of the oblique groove on the posterior surface of the bone, through which the 

 tendon of the Extensor longus pollicis runs, and serves to keep that tendon in its place. 



Surgical Anatomy. The two bones of the forearm are more often broken together than is 

 either the radius or ulna separately. It is therefore convenient to consider the fractures of these 

 two bones together in the first instance, and subsequently to mention the principal fractures 

 which take place in each bone individually. These fractures may be produced by either direct 

 or indirect violence, though more commonly by direct violence. When indirect force is applied 

 to the forearm the radius generally alone gives way, though both bones may suffer. The 

 fracture from indirect force generally takes place somewhere about the middle of the bones ; 

 fracture from direct violence may occur at any part, more often, however, in the lower half of 

 the bone. The fracture is usually transverse, but may be more or less oblique. A point of 

 interest in connection with these fractures is the tendency that there is for the two bones to unite 

 across the interpsseous membrane; the limb should therefore be put up in a position midway 

 between supination and pronation, which is not only the most comfortable position, but also sep- 

 arates the bones most widely from each other, and therefore diminishes the risk of the bones 

 becoming united across the interosseous membrane. The splints, anterior and posterior, which arc 



Unites with shaft 

 about 20th year. 



Lower extremity. 



Fir,. 103. Plan of the development of 

 the radius. Bv three centres. 



