UNION OF RADIUS AND ULNA. 



and forearm ; and the posterior and internal lateral ligaments are 

 stretched. 



In extension,, the ulna and radius move on the articular surface extending, 

 of the humerus until they come into a line with the arm-bone. 

 This movement is checked by the anterior ligament, and the muscles 

 on the front of the joint. 



UNION OF THE RADIUS AND ULNA. The radius is connected Radius is 

 with the ulna at both ends by means of synovial joints and stir- jjjj^ to 

 rounding ligaments ; and the shafts of the bones are united by 

 interosseous ligaments. 



UPPER RADIO-ULNAR ARTICULATION. In this joillt the head of at the upper 



the radius is received into the small sigmoid cavity of the ulna, and end by 

 is kept in place by the following 

 ligamentous band : 



The annular or orbicular liga- 

 ment (fig. 40, a) is about one- 

 third of an inch wide, and is 

 stronger behind than before ; it 

 i> placed around the prominence 

 of the head of the radius, and is 

 attached to the anterior and pos- 

 terior edges of the small sigmoid 

 cavity of the ulna. Its upper 

 border, the thicker, is connected 

 with the ligaments of the elbow- 

 joint ; but the lower is free, and 

 is applied around the neck of the 

 radios. In the socket formed by 

 this ligament and the cavity of 

 the ulna the radius moves freely. 



The synovial membrane is a 

 prolongation of that lining the 

 elbow-joint ; it projects inferiorly 

 between the neck of the radius and the lower margin of the annular 

 ligament. 



LIGAMENTS OF THE SHAFTS OF THE BONES. The aponeurotic Union of the 

 stratum connecting together the bones nearly their whole length 

 consists of the two following parts : 



The interosseous membrane (fig. 39, 3 ) is a thin fibrous layer, which interosseous 

 is attached to the contiguous margins of the radius and ulna, and m 

 forms an incomplete septum between the muscles on the front and 

 Iwck of the forearm. Most of its fibres are directed obliquely 

 down wards and inwards, though a few on the posterior surface have 

 an opposite direction. Superiorly, the membrane is wanting for a is deficient 

 considerable space, and through the interval the posterior inter- a 

 osseous vessels pass backwards. Some small apertures exist in it 

 for the passage of vessels ; and the largest of these (*) is about two 

 inches from the lower end, through which the anterior interosseous 

 artery turns to the back of the wrist. The membrane gives 

 attachment to the deep muscles. 



D.A. H 



FIG. 40. VIEW OF THE ORBICULAR 

 LIGAMENT (), WHICH RETAINS 

 THE UPPER END OF THE RADIUS synovial 

 AGAINST THE ULNA. membrane. 



