RADIUS. 189 



immediately on the inside of the ridge, the tendon of the 

 extensor of the last joint of the thumh plays. In a large one, 

 inside of this, the tendons of the indicator, and of the common 

 extensor muscles of the fingers pass. On the outside of the 

 ridge there is a broad depression, which seems again subdivided, 

 where the two tendons of the extensor carpi radialis are lodged. 

 The external side of this end of the radius is also hollowed 

 by the extensors of the first and second joints of the thumb. 

 The ridges at the sides of the grooves, in which the ten- 

 dons play, have an annular ligament fixed to them, by which 

 the several sheaths for the tendons are formed. The forepart 

 of this end of the radius is also depressed, where the flexors of 

 the fingers and flexor carpi radialis pass. The internal side is 

 formed into a semilunated smooth cavity, lined with a cartilage, 

 for receiving the lower end of the ulna. The lowest part of 

 the radius is formed into an oblong cavity ; in the middle of 

 which is a small transverse rising, gently hollowed, for lodging 

 mucilaginous glands ; while the rising itself is insinuated into 

 the conjunction of the two bones of the wrist that are received 

 into the cavity. The external side of this articulation is defended 

 by a remarkable process of the radius, from which a ligament 

 passes to the wrist ; and this structure resembles that of the 

 styloid process of the ulna with its ligament. 



The ends of both the bones of the forearm being thicker than 

 the middle, and the radius being curved, there is a considerable 

 distance between the bodies of these bones ; in the larger part of 

 which a strong, tendinous, but thin ligament, is extended, to give 

 a sufficient surface for the origin of the numerous fibres of the 

 muscles situated here, that are so much sunk between the bones 

 as to be protected from injuries, to which they would otherwise 

 be exposed. But this ligament is wanting near the upper end 

 of the forearm, where the supinator radii brevis and flexor digi- 

 torum profundus, are immediately connected. 



As the head of the radius receives the tubercle of the os 

 humeri, it is not only bended and extended along with the ulna, 

 but may be moved almost half round its axis ; and that this 



