RADIOULNAR ARTICULATION 



311 



ORBICULAR LIGAMENT 

 OF RADIUS 



TENDON OF 

 BICEPS MUSCLE 



(cut through) 



circumference than above, by which means the head of the radius is more securely 

 held in its position. Its outer surface is strengthened by the external lateral 

 ligament of the elbow, and affords 

 origin to part of the Supinator [brevis] 

 muscle. Its inner surface is smooth, 

 and lined with synovial membrane. 

 The synovial mem brane is continuous 

 with that which lines the elbow-joint. 



Movements. The movement which takes 

 place in this articulation is limited to rotation 

 of the head of the radius within the orbicular 

 ligament, and upon the lesser sigmoid cavity 

 of the ulna ; the axis of rotation passes through 

 the centre of the capitellum of the radius. 

 Rotation forward is called pronation; rota- 

 tion backward, supination. Supination is 

 performed by the Biceps and Supinator 

 [brevis], assisted to a slight extent by the Ex- 

 tensor muscles of the thumb and, in certain 

 positions, by the Brachioradialis. Pronation 

 is effected by the Pronator teres and Pronator 

 quadratus, assisted, in some positions, by the 

 Brachioradialis. 



Surface Form. The position of the su- 

 perior radioulnar joint is marked on the 

 surface of the body by the little dimple on 

 the back of the elbow, which indicates the 

 position of the head of the radius. 



Applied Anatomy. Dislocation of the 

 head of the radius alone is not an uncommon 

 accident, and occurs most frequently in young 

 persons from falls on the hand when the fore- 

 arm is extended and supinated, the head of 

 the bone being displaced forward. It is at- 

 tended by rupture of the orbicular ligament. 

 Occasionally a peculiar injury, which is sup- 

 posed to be a subluxation, occurs in young 

 children in lifting them from the ground by 

 the hand or forearm. It is believed that the 

 head of the radius is displaced downward or 

 the orbicular ligament upward, and the upper 

 border of the ligament becomes folded over 

 the head of the radius, between it and the 

 capitellum of the humerus. 



INTEROSSEOUS 

 MEMBRANE' 



2. MIDDLE RADIOULNAR LIGAMENTS. 



The interval between the shafts of 

 the radius and ulna is occupied by two 

 ligaments. 



Oblique. 

 Interosseous. 





STYLOID 

 .PROCESS 

 OF ULNA 



[TRIANGULAR 

 ARTICULAR 



DISK 



_STYLOID PROCESS 

 OF RADIUS 



The Oblique ligament (chorda obli- FlG - 202. Bones of the right forearm, with their liga- 

 >. /T -v i r,- merits; volar aspect. (Spalteholz.) 



gua) (Figs. 248 and 2o2) is a small, flat- 

 tened fibrous band which extends obliquely downward and outward from the 

 tubercle of the ulna at the base of the coronoid process to the radius a little below 

 the bicipital tuberosity. Its fibres run in the opposite direction to those of the 



