FOREARM AND HAND 171 



between the radial head of the first dorsal interosseous muscle and the 

 adductor pollicis. It arises from the ulnar side of the base of the first 

 metacarpal bone and is inserted into the ulnar side of the base of the 

 first phalanx of the thumb. It is supplied by a twig from the deep 

 division of the ulnar nerve. 



Arteria Volaris Indicis Radialis, et Arteria Princeps 

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

 These arteries spring from the radial, as it enters the 

 palm, between the first and second metacarpal bones. 



The volar radial artery of the index digit 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 digital artery. 



The princeps pollicis artery 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. There it lies dorsal to the tendon of the flexor 

 pollicis longus, and divides into two terminal branches, one 

 for each side of the free part of the thumb. The branches 

 make their appearance in the interval between the adductor 

 and the superficial head of the flexor pollicis brevis, and run 

 distally, one on each 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 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 proxi- 

 mally. The volar 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 seen to extend proximally 

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

 sheath is attacked by inflammatory action it is apt to become distended 

 with fluid (thecal ganglion), and the anatomical arrangement of the 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. There the dense transverse carpal ligament 

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



