THE HAND. 69 



153. Metacarpal joint of thumb. The joint of the 

 metacarpal bone of the thumb with the trapezium can be 

 distinctly felt by tracing the dorsal surface of the bone 

 upwards till we come to the prominence which indicates the 

 joint at the bottom of the ' tabatiere anatomique ' (140). Sup- 

 posing, however, there be much swelling, the knife introduced 

 at the angle between the first and second metacarpal 

 bones readily finds the joint if the blade be directed 

 outwards. 



1 54. Sesamoid bones. The sesamoid bones of the thumb 

 can be distinctly felt. Just above them that is, nearer to 

 the wrist lies the joint between the metacarpal bone and 

 the first phalanx. We should remember the position of 

 these bones in amputation at this joint. Mutatis mutandis 

 the same observations apply to the sesamoid bones of the 

 great toe. 



The extensor tendon of the last joint of the thumb crosses 

 the apex of the first interosseous space. Under the tendon, 

 and in the angle between the bones, we feel the radial artery 

 just before it sinks into the palm. 



155. Subcutaneous veins. The veins on the back of the 

 hand, and their arrangement in the form of arches which 

 receive the digital veins, is sufficiently obvious. The number 

 and arrangement of the arches may vary, but in all hands it 

 is interesting to notice that the veins from the fingers run up 

 between the knuckles and are out of harm's way. 



156. Znterosseous arteries. Since the dorsal interos- 

 seous arteries, like the palmar, run along the interosseous 

 spaces, incisions to let out pus should always be made along 

 the lines of the metacarpal bones. 



157. Digital bursae. Small subcutaneous bursae are 

 sometimes developed over the knuckles and the backs of the 

 joints of the fingers. They often become enlarged and un- 

 seemly in persons of a rheumatic or gouty tendency. 



158. Knuckles and digital joints. The three rows of 

 projections called ' the knuckles ' are formed by the proximal 

 bones of the several joints : thus the first row is formed by 

 the ends of the metacarpals ; the second by the ends of the 



