SKELETON. 



the trapezium, in flexion, extension, adduction, abduction: and 

 circumduction is the result of the other four. In consequence 

 of this variety of movement in it, of its position on a plane an- 

 terior to that of the fingers, and of a corresponding obliquity 

 of the trapezium, the thumb can, in all cases of grasping and 

 examining bodies, antagonize the fingers. The circumduction 

 of the thumb resembles very much that of the wrist, or shoul- 

 der joint, though the mechanism of the articular surfaces is dif- 

 ferent. In this motion, it describes a cone or circle, the ante- 

 rior segment of which is larger, and performed with more fa- 

 cility than the posterior. 



The second and third metacarpal bones are so closely bound 

 to the carpus, that their motion above is almost imperceptible; 

 in consequence of their length, the motion is more appreciable 

 below, but even there it is very much restricted. The fourth 

 metacarpal bone has a limited ginglymous movement, which is 

 sufficiently demonstrable, and the fifth has it in a considerable 

 degree; it also admits of a sort of adduction, by which it is 

 brought nearer to the other bone. 



The first phalanges admit of flexion, extension, adduction, ab- 

 duction; and circumduction, by the successive performance of 

 the others. The first phalanx of the thumb has the three last 

 motions very much curtailed, in consequence of the necessity 

 of great strength and stability in this joint, so as to antagonize 

 firmly the fingers. The remaining phalanges perform, simply, 

 flexion and extension. The latter, as in the knee and elbow, 

 rarely goes beyond the axis of the limb, whereas the former, 

 from the extent of the articular surfaces and the particular me- 

 chanism of the joint, permits the hand to be closed and dou- 

 bled. 



From what has been said, it will not be difficult to form $ 

 general conception of the great variety of motions resulting 

 from the number and arrangement of the pieces constituting 

 the upper extremity. The os humeri being the basis of them, 

 may be presented in any direction; the bones of the fore arm 

 may be alternately retracted or protruded, and by the revolving 

 of the radius, will permit the palm of the hand to apply itself at 



