FOREARM AND HAND 131 



Arteria Volaris Indicis Radialis, and Arteria Princeps 

 Pollicis (O.T. Radialis Indicis and Princeps Pollicis Arteries). 

 These arteries spring from the radial as it proceeds towards 

 the volar surface between the first and second metacarpal 

 bones. 



The arteria volaris indicts radialis runs distally between the 

 transverse part of the adductor pollicis and the first dorsal 

 interosseous muscle to the lateral border of the index, along 

 which it proceeds as its lateral volar proper digital artery. 



The arteria princeps pollicis takes a course distally and 

 laterally under cover of the oblique part of the adductor 

 pollicis, and gains the volar aspect of the metacarpal bone of 

 the thumb. Here it lies dorsal to the tendon of the flexor 

 pollicis longus, and divides into the volar proper digital 

 arteries of the thumb. These branches make their appear- 

 ance in the interval between the adductor and the superficial 

 head of the flexor pollicis brevis, and are carried distally on 

 either side of the tendon of the long flexor. 



Surgical Anatomy of the Palm and Fingers. When an abscess forms 

 in the intermediate compartment of the palm early surgical interference is 

 urgently called for. The dense palmar aponeurosis effectually prevents the 

 passage of the pus to the surface of the palm, whilst an easy route proximally 

 into the forearm is offered to it by the open carpal tunnel, through which 

 the flexor tendons enter the palm. It is absolutely necessary, therefore, 

 that before this can occur the surgeon should make an opening in the 

 palm by means of which the pus can escape. 



In making such an incision it is important to bear in mind the position of 

 the various vessels which occupy the intermediate compartment of the palm. 

 As previously stated, the level of the superficial volar arch can be indicated 

 by drawing a line transversely across the palm from the distal margin of the 

 outstretched thumb. The deep volar arch lies half an inch more proximally. 

 The volar common digital arteries, which spring from the convexity of the 

 superficial volar arch, run in line with the clefts between the fingers. An 

 incision, therefore, which is made distal to the superficial volar arch and in 

 a direction corresponding to the central line of one of the fingers, may be 

 considered free from danger in so far as the vessels are concerned. 



The loose mucous sheath which envelops the flexor tendons as they pass 

 deep to the transverse carpal ligament has been noticed to extend proxim- 

 ally into the distal part of the forearm, and distally into the palm. 

 When this is attacked by inflammatory action it is apt to become distended 

 with fluid (thecal ganglion), and the anatomical arrangement of parts at 

 once offers an explanation of the appearance which is presented. There is 

 a bulging in the palm, and a bulging in the distal part of the forearm, but 

 no swelling at all at the wrist. Here the dense transverse carpal ligament 

 resists the expansion of the mucous sheath, and an hour-glass constriction 

 is evident at this level. 



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, 

 i 9 a 



