THE RADIUS. 



261 



Head. 



Appears at r^^g-^^ Unites with shaft 

 5th year. ~^B^"V about puberty. 



Appears at_ 

 2<l year. 



Unites with shaft 

 about SOth year. 



Lower extremity. 



FIG. 203. Plan of the development of 

 the radius. By three centres. 



soon after the development of the humerus commences. At birth the shaft is 



ossified, but the ends of the bone are cartilaginous. About the end of the second 



year ossification commences in the lower epiph- 



ysis and about the fifth year in the upper one. 



At the age of seventeenoreighteen the upper epiph- 



ysis becomes joined to the shaft, the lower epiph- 



ysis 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 maybe 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 

 tli is dimple and the forearm pronated and supinated, 

 the head of the bone will be distinctly perceived rotating 

 in the lesser sienioid 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 bounds the 

 oblique groove on the posterior surface of the bone, through which the tendon of the Rxtensor 

 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 interosseous 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 are 

 applied in these cases should be rather wider than the limb, so as to prevent any lateral pressure 

 on the bones. For in these cases there is a greater liability to gangrene from the pressure of the 

 splints than in other parts of the body. This is no doubt due principally to two causes : (1) 

 the flexion of the forearm compressing to a certain extent the brachial artery and retarding the 

 flow of blood to the limb : and ( 2) the superficial position of the two main arteries of the forearm 

 in a part of their course, and their liability to be compressed by the splints. The special 

 fractures of the ulna are (1 ) Fracture of the olecranon. This may be caused by direct violence, 

 falls on the elbow with the forearm flexed, or by muscular action by the sudden contraction of 

 the triceps. The most common place for the fracture to occur is at the constricted portion 

 where the olecranon joins the shaft of the bone, and the fracture may be either transverse or 

 oblique ; but any part may be broken, even a thin shell may be torn off. Fractures from direct 

 violence are occasionally comminuted. The displacement is sometimes very slight, owing to the 

 fibrous structures around the process not being torn. (2) Fracture of the coronoid process some- 



