SURGICAL ANATOMY OF THE PALM. 167 



ing the knife is the second fold in the skin seen on the 

 dorsal aspect of the joint. 



The vessels and nerves supplying the fingers, includ- 

 ing the thumb, are derived from the digital branches of 

 the radial and ulnar arteries, and ulnar and median 

 nerves, the former supplying the thumb and radial side 

 of the index, the ulnar side of the index, and remaining 

 fingers; and the latter the little finger, half the ring 

 finger, and the remaining fingers. The arteries anasto- 

 mose very freely in the pulp and matrix of nail. The 

 veins accompany the arteries and pass posteriorly, and 

 form a considerable plexus, passing along the back of 

 the fingers into the veins of the back of the hand. 



Dislocation of the first phalanx of the thumb is diffi- 

 cult of reduction, and if reduced, of being maintained 

 in position, owing to the great power exerted by the 

 mass of muscles forming the ball of the thumb, and to 

 the fact that when the phalanx lies on the dorsal aspect 

 of the metacarpal bone, the narrow head of the latter be- 

 comes constricted by the two terminal attachments of 

 the flexor brevis pollicis, the tendons of which are fur- 

 ther strengthened by the conjoined insertion of the ad- 

 ductor and abductor. 



