THE ANTERIOR RADIOULNAR REGION 209 



The index finger portion is usually separate throughout, 

 and comes mostly from the interosseous membrane; between 

 the ring and little finger portions a considerable part of the 

 inner surface of the ulna is free from muscular attachment. 



The sheaths of the flexor tendons are opposite the proximal 

 and middle phalanges, and formed of strong transverse bands, 

 ligamenta vaginalia; opposite the joints the bands change into 

 a thin membrane, strengthened by oblique decussating fibers, 

 so that there are annular or transverse fibers, and crucial or 

 oblique. The sheath has a synovial lining containing small 

 folds, mncula tendinum or ligamenta mucosa, passing between 

 the tendons and bones. There are two sets ligamenta brevia, 

 broad, four-sided, and membranous, passing between both 

 the superficial and the deep tendons near their insertions 

 and the lower part of the phalanx just above the joint capsule; 

 the ligamenta long a, less constant, join the tendons at a higher 

 level. Contained in the ligamentum breve of the deep flexor 

 is a small band of yellow elastic tissue, ligamentum subflavum, 

 passing from the tendon to the head of the second phalanx. 



2. M. flexor longus pollicis rises from the anterior surface 

 of the radius, below its oblique line to the edge of the pronator 

 quadratus, and from the adjacent part of the interosseous 

 membrane, and usually (27 out of 36 cases) receives a slip 

 (fasciculus exilis) from the inner epicondyle or coronoid. The 

 tendon passes between the sesamoid bones of the thumb and 

 enters a canal similar to that of the other flexors, to be inserted 

 into the base of the distal phalanx of the thumb. Its com- 

 plete separation from the flexor profundus is characteristic 

 of man. 



3. M. pronator quadratus, just above the wrist, close to the 

 bones behind the last two muscles, quadrilateral and flat, 

 arises from the pronator ridge and inner part of the anterior 

 surface of the ulna for the lower fourth, and from the inferior 

 from the radiocarpal joint; inserted into the anterior surface 

 and anterior margin of the shaft of the radius for a little less 

 than its fourth. 



Nerves. Six and one-half of the above muscles by the 

 median nerve, one and one-half by the ulnar. Pronator teres, 

 flexor carpi radialis, palmaris longus, and condyloulnar head 

 of the flexor sublimis receive median branches near the elbow; 

 radial head of the flexor sublimis and belly for the index finger 

 14 



