122 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 198. — The left elbow-joint seen from in front (f). 



Fig. 199. — The left elbow-joint seen from behind and from the radial side (§). 



Fig. 200. — The bones of the left forearm with the interosseous membrane; the annular ligament has 

 been divided (§). 



riorly than posteriorly; raising and lowering of the arm in a coronal plane (abduction and adduction, the former motion 

 not being possible beyond a horizontal plane); and rotation of the arm about its longitudinal axis. During the move- 

 ments of the arm the capsular ligament is thrown into folds upon one side and made tense upon the other and in certain 

 extreme positions it may act as a check ligament. 



THE ELBOW-JOINT. 



The elbow-joint is a typical compound joint, being formed by the association of the lower 

 end of the humerus with the upper ends of the radius and ulna, and so consisting of 

 three articulations. The trochlea of the humerus articulates with the semilunar (greater sigmoid) 

 notch of the ulna (the hiimero-ulnar articulation), the capitulum of the humerus with the 

 depressed surface on the head of the radius (the humero-radial articulation), and the radial (lesser 

 sigmoid) notch of the ulna with the articular circumference of the radius (the proximal radio- 

 ulnar articulation). 



The three articulations are surrounded by a common articular capsule (Figs. 198 and 199), 

 which is roomy and relaxed, particularly in front and behind. It encloses the three fossae at 

 the lower end of the humerus (the olecranal, coronoid, and radial fossae), is attached to fie ulna 

 just below the tip of the olecranon, at the margin of the semilunar (greater sigmoid) notch, and 

 at the tip of the coronoid process, and the entire head and the greater portion of the neck of 

 the radius are situated within it. The only portions of it which are firm and tense are the lateral 

 ligaments and the annular ligament which surrounds the upper end of the radius. 



There may be recognized a radial or external lateral ligament and an ulnar or internal 

 lateral ligament. The radial lateral ligament (Figs. 198 and 199) arises from the external epicon- 

 dyle and passes as two fasciculi to the annular ligament, with which a portion of its fibers are 

 continuous. The ulnar lateral ligament (Fig. 198) arises from the internal epicondyle of the 

 humerus and passes in a radiating manner to the ulnar margin of the semilunar notch. 



The annular ligament (Fig. 199) is a firm tense ligament which surrounds the head of the 

 radius like a sling and forms three-fourths of the circumference of the socket for the pivot joint 

 of the proximal radio-ulnar articulation, the remaining fourth being formed by the radial (lesser 

 sigmoid) notch of the ulna. The ligament arises from the anterior margin of the semilunar 

 (greater sigmoid) notch and is inserted into the posterior margin of the radial notch. Below 

 it the capsule is thin, and at the neck of the radius forms a small protrusion which is known 

 as the saccular recess. 



The brachialis anticus muscle passes over the anterior surface of the capsular ligament of 

 the elbow-joint (Fig. 201) and some of its fibers are inserted directly into this structure. The 

 triceps muscle, particularly its middle head, holds a similar relation to the posterior surface of 

 the capsule, from which the tendon of the muscle is separated by fatty tissue. 



