ARTICULATION OF THE WRIST. 



249 



Fig. 56.* The motion of the ulna and radius on the 



os humeri is that of the simple flexion and 

 extension. The cylindrical head of the Radius 

 performs a part of a revolution, nearly on its 

 own axis, without moving from the depression 

 in the side of the ulna, with which it is in 

 contact. 



The synovial membrane adheres very firmly 

 to the surface covered with cartilage on each 

 of the bones, and is reflected from the margin 

 of this surface, on one bone, to that of the 

 others. As the principal motion performed is 

 hinge-like, the principal ligaments are on the 

 sides. There is also a circular ligament, which 

 arises from the ulna and invests the narrow part 

 of the radius immediately below its cylindrical 

 head like a loop, to confine the radius in 

 contact with the ulna, and at the same time 

 permit its motion. 



This ligament is so blended with the synovial membrane, that 

 it sometimes cannot be separated from it. 



The lateral ligaments are denominated from their origin and 

 insertion, Brachio-radial, and Brachio-cubital, or External and 

 Internal. The external is a strong, narrow band, attached 

 above to the external condyle of the humerus, and below 

 to the orbicular ligament, and adjoining ridge of the ulna. 

 The internal, is thick and triangular ; its apex is attached to 

 the internal condyle of the humerus, and its lower or broad 

 part is inserted into the margin of the greater sigmoid fossa of 

 the ulna extending from the coronoid process to the olecra- 

 non. Posterior to it runs the ulnar nerve. The ligament 

 which invests the neck of the radius is called Coronary or 

 Orbicular. 



* An internal view of the ligaments of the elbow joint. 1. The anterior 

 ligament. 2. The internal lateral ligament. 3. The orbicular ligament. 4. The 

 oblique ligament. 5. The interosseous ligament. 6. The internal condyle of 

 ihe humerus, which conceals the posterior ligament. 



