

Interosseous Membrane 285 



middle, or lower third. What may be called the ' favourite situation ' 

 is just below the middle, so that the stump may be left under the 

 government of the pronator radii teres as well as of the supinator brevis 

 and its powerful ally, the biceps. 



In amputation at the wrist the flap is dissected from the palm, and 

 turned back over the lower end of the radius and the triangular fibro- 

 cartilage. The head of the ulna and the membrana sacciformis are 

 not exposed or interfered with. 



Below the level of the superior radio-ulnar joint the bones of the 

 fore-arm are connected by an oblique ligament which runs downwards 

 from the coronoid process of the ulna to the radius, just below the 

 tuberosity. Then begin the fibres of the interosseous membrane, 

 which are oblique in the other sense, namely, downwards and inwards. 

 Between the upper border of the interosseous membrane and the 

 oblique ligament is a triangular gap through which the posterior inter- 

 osseous vessels pass ; the nerve, however, reaches the back of the 

 fore-arm by passing round the outer side of the radius through the 

 supinator brevis. 



Relations of the membrane. Upon the front lie the origins of the 

 flexors profundus digitorum and longus pollicis, and deep in the interval 

 between them run the anterior interosseous vessels and nerve. The 

 pronator quadratus covers its lower third. 



Upon the posterior surface rest the supinator brevis and the origins 

 of the three extensors of the thumb and of the index-finger. Because 

 of these oblique extensors covering the membrane, the posterior 

 interosseous vessels do not reach it, but the anterior interosseous 

 artery, which comes through above the pronator quadratus, and the 

 ending of the posterior interosseous nerve, lie upon it just above the 

 wrist. 



The inferior radio-ulnar joint consists of the lesser sigmoid cavity 

 of the radius, and the head of the ulna. These surfaces are covered 

 with cartilage and lubricated with a loose synovial membrane (sacci- 

 formis}, and are connected in front and behind by short bands of 

 fibres. 



Extending from the root of the styloid process of the ulna to the 

 lower border of the lesser sigmoid cavity of the radius is the triangular 

 Jibro-cartilage, which shuts the ulna out of the wrist-joint. The lower 

 surface of this cartilage articulates with the cuneiform, and is lubricated 

 by the synovial membrane of the wrist-joint. Sometimes the synovial 

 membranes above and below the joint blend through a hole in the carti- 

 lage. (See next page.) 



The joint is supplied by branches of the two interosseous arteries 

 and nerves. 



The wrist-joint is formed above by the radius and the triangular 

 inter-articular fibre-cartilage, and below by the scaphoid, semilunar, 

 and cuneiform bones, the last-named articulating with the fibro-carti- 



