THE RADIUS 



47 



magnus, extensor pedis, and extensor metacarpi obliquus muscles respec- 

 tively play. 



The posterior surface is almost flat. Towards its outer side is an 

 elongated triangular roughened area, the apex of which is directed down- 

 wards, and to which the ulna is united. Above this area is a transverse 

 smooth depression which forms the anterior boundary of the radio-ulnar 

 arch. In this depression is found the nutrient foramen. Above the radio- 

 ulnar arch the bone shows a roughened area to which is attached another 

 interosseous ligament uniting it to the ulna. Near this spot also there are 

 two small facets which form synovial joints with like facets on the 

 ulna. The supracarpal band, sometimes called the check band of the 

 perforatus, is attached to a roughened elongated elevation which is placed 

 in the inferior third of the posterior surface and towards the inner side. 



The upper surface of the bone is articular, and moulded on to the 

 inferior surface of the humerus. The edge of this surface is elevated 

 near the middle line anteriorly to form the coronoid process. The inferior 

 surface is likewise articular. It presents three facets, the innermost of 

 which is concavo-convex from before backwards and responds to the 

 upper surface of the scaphoid. The middle one is similarly concavo- 

 convex, but is much smaller, and is for articulation with the semilunar 

 bone. The remaining facet is convex, and its outline approaches the 

 elliptical. This facet articulates with the cuneiform. Above this facet, 

 on the posterior aspect of the bone, is a small facet which articulates with 

 the upper of the two facets on the pisiform bone. Above the facets just 

 described, the posterior surface presents an irregular prominent and 

 roughened transverse ridge, which affords the superior attachment to the 

 posterior common ligament of the knee. 



At either extremity the radius is expanded, and outwardly and 

 inwardly each end is tuberous and roughened for ligamentous attachment. 

 The bone narrows down considerably towards the middle of its diaphysis. 



From an inch to an inch and a half below its upper articular surface 

 there is a groove on the inner side which runs backwards and slightly 



