REGION OF THE ELBOW. 283 



LIGAMENTS OF THE ELBOW. 



The ligaments of the elbow-joint are four in number anterior, posterior, internal 

 lateral, and external lateral. 



In all joints there are two kinds of ligaments. One kind serves to retain the 

 synovial fluid; it is a capsular ligament and is usually thin; the other kind is thick, 

 firm, and strong, and is intended to bind the bones together and prevent their dis- 

 placement and to limit movement. These two kinds of ligaments often blend 

 together so that it is impossible to say where one begins and the other ends ; at other 

 places they are quite distinct. If an elbow-joint is distended with effusion (or wax) 

 the distinction is readily seen. The capsule becomes distended in front and behind, 

 while at the sides the ligaments remain closely applied to the bones ; hence we learn 

 that the anterior and posterior ligaments are capsular in their function while the 

 lateral ligaments are retentive. These will be considered more in detail later. 



Superior Radio-ulnar Articulation. While the superior radio-ulnar articula- 

 tion is not considered a part of the elbow-joint proper, it is nevertheless so closely 



FIG. 295. The external lateral ligament of the elbow- joint, showing its A shape. Its upper end is attached 

 to the external condyle of the humerus; its lower ends are attached to the ulna. The circular fibres surrounding 

 the head of the radius are called the orbicular ligament. 



associated with it that it cannot be ignored. The head of the radius, in addition to 

 its movements of flexion and extension on the humerus, possesses a motion of rotation. 

 In order that it may rotate properly the ligaments are arranged in a peculiar manner. 

 Its motion in respect to the ulna is a purely rotary one, so that it is bound to the 

 ulna by a ligament which encircles its head, called the orbicular ligament. The 

 bulk of the ligament encircles three-fourths of the head of the radius and is attached 

 at its ends to the anterior and posterior edges of the lesser sigmoid cavity of the ulna. 

 Its lower fibres are continuous below the lesser sigmoid cavity, forming a complete 

 circle. The upper edge of this orbicular ligament blends with the anterior ligament 

 in front, the posterior behind, and the external lateral at the side. We thus see that 

 as the anterior and posterior ligaments are capsular in their function the radius is 

 kept in place by the external lateral ligament, which branches below in the form of 

 the letter Y to blend with the orbicular ligament. When we consider that these 

 fibres are hardly inserted at all into the radius, but pass over it to the ulna, it is 

 evident that this part of the joint is comparatively weak and not an excessive amount 

 of force would be required to pull the head of the radius from beneath the orbicular 



