172 THE SUPERIOR EXTREMITY 



is evident at that level. The lines along which incisions should be made 

 into the volar compartments of the palm and the mucous sheaths of the 

 flexor tendon are shown in Fig. 71. 



The fingers are subject to an inflammatory process, termed whitlow, 

 and, in connection with this, it is essential to remember that the flexor 

 fibrous sheath ends on the base of the distal phalanx in each digit. 

 When the whitlow occurs more distally, in the pulp of the finger, the vitality 

 of the distal part of the ungual phalanx is endangered, but the flexor 

 tendons may be regarded as being tolerably safe. When the inflammation 

 occurs more proximally, and involves the flexor sheath, as it generally does, 

 sloughing of the tendons is to be apprehended, unless an immediate 

 opening is made. No slight superficial incision will suffice. The 

 knife must be carried deep into the centre of the finger, so as to freely 

 lay open the sheath containing the tendons. Early interference in cases 

 of whitlow of the thumb and little finger is even more urgently required 

 than in the case of the other three digits, because the digital mucous 

 sheaths of the former are, as a rule, connected with the great common 

 mucous sheath of the flexor tendons, and so offer a ready means for the 

 proximal extension of the inflammatory action. 



Every amputation of the fingers proximal to the insertion of the tendons 

 of the flexor profundus involves the opening of the flexor sheaths, and no 

 doubt explains the occasional occurrence of palmar trouble after operations 

 of that kind. The open tubes offer a ready passage by means of which 

 septic material may travel proximally into the palm, and, in the case of 

 the thumb and little finger, into the carpal tunnel and distal part of the 

 forearm. 



DORSUM AND LATERAL BORDER OF THE FOREARM. 



The structures which still remain to be dissected in this 

 region are : 



1. The supinator and extensor muscles. 



2. The dorsal interosseous artery. 



3. The perforating or terminal branch of the volar interosseous artery. 



4. The dorsal interosseous nerve. 



Before the dissection is proceeded with, the cutaneous 

 veins and nerves and the deep fascia, previously displayed, 

 should be re-examined. The two main cutaneous veins 

 are seen. Both ascend from the venous plexus on the 

 dorsum of the hand, and both turn round a border of the 

 forearm to gain its volar surface, but whilst the cephalic 

 vein turns round the distal third of the radial border, the 

 basilic ascends to a much more proximal level before it 

 turns round the ulnar border. 



The cutaneous nerves are four in number: (i) The 

 dorsal branch of the lateral cutaneous nerve of the forearm, 

 on the lateral side ; (2) the dorsal branch of the medial 

 cutaneous nerve of the forearm on the medial side ; (3) in the 



