188 RADIUS. 



Radius. 



Before the radius is described, it is necessary to observe that the lower end of 

 this bone occasionally revolves half round the lower end of the ulna, and the 

 hand with it. The relative situation of these parts is, therefore, different in 

 different positions of the hand. In the following description, the palm of the 

 hand is supposed to present forwards, and the thumb outwards j in which case, 

 the two bones of the forearm will be parallel to each other. 



The radius is situated on the outside of the forearm, and is 

 rather shorter than the uhia. Its eKtremities are the reverse of 

 those of the ulna in their proportionate size ; and the body is 

 not triangular, although it approaches towards that form. Its 

 upper end is formed into a cylindrical head, which is hollowed 

 on the top for an articulation with the tubercle at the side of 

 the pulley of the os humeri ; and the half cylindrical circum- 

 ference next to the ulna is smooth, and covered with a carti- 

 lage, in order to be received into the semilunated cavity of that 

 bone. Below the head, the radius is much smaller; and, there- 

 fore, this part is named its cervix. At the internal root of this 

 neck is a flat tubercle, into the inner part of which the biceps 

 flexor cubiti is inserted. From this a ridge runs downwards and 

 outwards where the supinator radii brevis is inserted ; and a little 

 below, and behind this ridge, there is a rough scabrous surface, 

 where the pronator radii teres is fixed. 



The body of the radius is not straight, but curved externally 

 the greater part of its length. Its external surface is rounded ; 

 the anterior and posterior surfaces are flattened ; and between 

 them is a sharp spine, to wiiich the strong ligament extended 

 between the two bones of the foreartu is fixed. On the ante- 

 rior surface, at a distance from its head, nearly equal to one- 

 third the length of the bone, is the orifice of the canal for 

 the medullary vessels, which has a direction obliquely up- 

 wards. 



Towards the lower end the radius becomes broader and 

 flatter, especially on its forepart, where the pronator quadratus 

 muscle is situated. Its back part, at this end, has a flat strong 

 ridge in the middle, and fossa; on each side. In a small groove, 



