MOVEMENT OF THE LOWER END OF THE RADIUS. 107 



by pushing the radius upwards while the ulna is kept fixed, 

 or by pulling the ulna downwards when the radius is kept 

 fixed. 



It has long been recognised that the interosseous membrane 

 plays an important part in transmitting to the ulna any force 

 acting upwards through the radius, and, conversely, in trans- 

 mitting to the radius a downward thrust on the part of the 

 ulna. A good account of this action of the interosseous mem- 

 brane, and of the anatomical conditions which make it neces- 

 sary, will be found in Morris's Anatomy of the Joints, 1879, 

 p. 260. See also Holden, Human Osteology, 1887, p. 316. 



In this function the interosseous membrane is assisted mate- 

 rially by the triangular ligament, to whose action in receiving 

 the thrust of the lower end of the ulna, Professor Clelaud 

 attracts my attention as all the more worthy of remark, now 

 that it is known by means of skiagraphs how little support the 

 ulna gets from the cuneiform bone. In this connection it is 

 worth remembering that in some animals the interosseous mem- 

 brane and the triangular ligament are continuous with one 

 another, the place of the inferior radio-ulnar joint being taken 

 by fibrous tissue. (See F. G. Parsons in Journ. of Anat. and 

 Phys., Oct. 1899.) 



From the direction of the fibres the main sheet of the inter- 

 osseous membrane is of little use in transmitting to the ulna a 

 downward pull on the radius. The so-called 'oblique' liga- 

 ments and the scattered fibres parallel to them in the rest of 

 the membrane run in the proper direction, but are compara- 

 tively weak. Under ordinary circumstances they are reinforced 

 by the muscles arising from the humerus and inserted into the 

 wrist and hand, which, when acting, suspend these parts 

 directly from the humerus as in a sling. If the muscles in 

 question be put out of action, the lifting power of the forearm 

 is greatly lessened. Suspend a moderately heavy weight by 

 means of a suitable loop round the wrist, at the same time 

 keeping the muscles of the forearm slack. In a short time 

 more or less acute discomfort will be felt at the outer and fore 

 part of the elbow joint. Some such result is to be expected, 

 seeing that the radius has not direct ligamentous connection 

 with the humerus. 



