ioo Anatomy Applied to Medicine a fid Surgery. 



of rotation due to the ball and socket formation of the 

 joint between the os magnum below and the scaphoid and 

 semilunar above. When the extended fingers are "bunch- 

 ed" the little and ring fingers move to the central point 

 more easily than do the middle and index fingers, and the 

 reasons for this are : (l)That the articulation, between the 

 unciform above and the metacarpal bones of the little and 

 ring fingers below, is directed slightly inwards; (2) that 

 there is greater freedom of movement permitted at the 

 above joints, than there is at the carpal articulations of 

 the other metacarpal bones, with the exception, of course, 

 of the thumb, which, being a concavo-convex joint, allows 

 movement in every direction. This shape of the joint for 

 the thumb explains what is called the "opposition" move- 

 ment, i.e., when the thumb is approximated to the fingers, 

 it tends to roll inwards so as to face the fingers. 



The wrist joint proper does not permit rotation since 

 it is a condyloid articulation, but pronation and supination 

 of the hand replace this movement of rotation. Prona- 

 tion and supination are the result of rotation of the radius 

 at the humero-radial joint, round an axis running down- 

 wards from the head of the radius through the styloid 

 process of the ulna and the metacarpal bone of the little 

 finger. In the practical application of pronation and su- 

 pination, as seen in the use of boring instruments, for in- 

 stance, there is another agent brought into play, and with- 

 out which, these movements would be very much limited, 

 and this agent is the shoulder joint. It will be noticed in 

 boring, etc., that, to supination is added adduction and 

 outward rotation of the humerus, while, to pronation there 

 is added abduction and inward rotation. This change of 

 position of the humerus, during supination and pronation 

 of the forearm, adds to the efficiency of these movements, 

 since it alters the situation of the base from which they 



