88 THE SUPERIOR EXTREMITY 



retro-tendinous pouch. The open space at the ulnar side of the 

 sheath, with which all three pouches communicate freely, is 

 termed the ulnar bursa. 



The median nerve is situated between the sheath of the 

 flexor pollicis longus and the common palmar sheath. 



Digital Synovial Sheaths invest the flexor tendons as they 

 lie in their osteo-fascial canals on the front of the fingers. They 

 extend distally as far as the insertion of the profundus tendons, 

 and proximally for half an inch beyond the metacarpo-phalangeal 

 joints. Ligamenta longa and brevia are present as in the case 

 of the flexor pollicis longus (Fig. 29). The digital synovial 

 sheath of the little finger is directly continuous with the common 

 palmar sheath, but the others are definitely closed at their 

 proximal ends. 



The following variations are described by Poirier. 



1. The index tendon of the profundus possesses a separate palmar sheath, 

 80 per cent. 



2. The flexor pollicis longus sheath communicates freely at its proximal 

 part with the common sheath, 50 per cent. 



3. The digital sheath of the little finger fails to communicate with the 

 common sheath, 35 per cent. 



4. The flexor pollicis longus sheath is in two separate parts, a digital and 

 a carpal, 5 per cent. 



Pus in the Common Palmar Sheath. The common 

 palmar sheath may be infected primarily by punctured wounds 

 of the palm or it may be involved secondarily, following a septic 

 infection either of the digital synovial sheath of the little finger 

 (Fig. 32) or of the middle palmar space (p. 90). Incisions into 

 the -proximal part of the sheath are made in the line of the ring 

 finger, and are limited distally by the distal skin crease at the 

 wrist. In this way no damage is done to the median nerve 

 which lies to the radial side of the incision or to the ulnar nerve 

 and artery, which lie to its medial side. Incisions into the distal 

 part of the sheath are made in the same line, but are limited 

 proximally by the distal border of the transverse carpal ligament 

 and distally by the superficial palmar arch. If the pus ruptures 

 the common palmar sheath and extends into the forearm, it 

 may be evacuated by incisions along the same line (Fig. 32). 



Compound Palmar Ganglion. This condition is a tuber- 

 culous synovitis affecting the common palmar sheath. It gives 

 rise to a dumb-bell-shaped swelling, which extends from the 

 distal part of the forearm into the palm, the constriction being 

 due to the transverse carpal ligament. Should a cold abscess 



