Bones of the Upper Extremity. 



101 



126. Right radius, radius, 



from behind. 



The upper extremity of the 

 radius supports the button - shaped 

 capitulum radii (head) ; this is for the 

 most part covered with cartilage and 

 proximalward presents a small flat 

 depression, fovea capituli radii (for 

 articulation with the capitulum humeri); 

 its circular periphery covered with car- 

 tilage, circumferentia articular is, mo- 

 ves in the incisura radialis ulnae. Just 

 below the capitulum the bone is narrowed 

 to form a neck, collum radii, and close 

 below this spot, projecting ulnarward and 

 volarward, is the tuberositas radii 

 (0. T. bicipital tuberosity) (for the 

 attachment of the m. biceps brackii). 



The lower extremity is mark- 

 edly broadened, quadrilateral. Its an- 

 terior surface is smooth and slightly 

 concave; its posterior surface is sub- 

 divided by several longitudinal ridges 

 into grooves for tendons (see Fig. 129). 

 The distal terminal surface, fades arti- 

 cularis carpea, covered with tough 

 fibrocartilage, is slightly concave and 

 triangular; it is subdivided, usually 

 distinctly, into a triangular radial part 

 (for the os naviculare) and a quadran- 

 gular ulnar part (for the radial portion 

 of the os lunatum). On the ulnar side 

 is a small notch covered with cartilage, 

 the incisura ulnaris (0. T. sigmoid 

 cavity) (for the capitulum ulnae and 

 the discus articularis). Projecting distal- 

 ward from the angle on the thumb side 

 is the short, blunt, quadrilateral-conical 

 processus styloideus. 



Circumferentia _ 

 articularis 



Collum radii 



Tuberositas __ .. 

 radii 



Capitulum radii 



Foramen nutricium 



Crista interossea 



Facies dorsalis 



Margo dorsalis 



Incisura ulnaris 

 Groove for the m. extensor 

 digitorum communis 



Groove for 

 the mm. ex- 



tensores 

 carpi radiales 



Groove for 

 the m. exten- 

 sor pollicis 

 I , longus 



Processus styloideus 



