CHRISTIANIA YIDEXSK.-SELSK. FORHANDL. 



1883. 



NO. 11. 



29 



of two chief necessities of movement, one of flexion and extension 

 of this segment of the limb. another of alteration of aspect of the 

 terminal segment or hand; the latter can scarcely be accomplished 

 in any other way than by semirotation. The conditions of powerful 

 flexion and extension are. on the contrary. best suited b}' a more 

 or less ginglimoid joint at each extremity; and the shape of the 

 interlocking surfaces which forms the chief secnrity of snch an 

 articulation, would render it insusceptible of this partial rotation. 

 These re([uirements. incompatible of fultilment by one bone. are 

 met by the addition of another, to which the hand is attached. 

 And now a new necessity arises; for the supperadded lever must 

 be associated with the pillar previously existing, so far as regards 

 the first movement, but dissevered from it as regards the second. 

 This is accomplished by giring the radius a very limited participa- 

 tion in the elbow joint, a very considerable one in the wrist; and 

 by making the ulna supply the terminal fixatures of the rotating 

 shaft. The peripheral and complet condition of the upper attache- 

 ment, the internal or centric and incomplete state of the lower, 

 which, like the shaft itself. is here reduced to a part of a circle; 

 these are provisions, which, like many met with in other parts of 

 the body, at once economise means and preserve the symmetry of* 

 the limb. — Pronation and supination. — The extremes of this 

 rotation of the lower extremity of the radius constitute the states 

 of pronation and supination. So far as these result from the 

 movements of this bone, the are not quite opposite aspects of its 

 surfaces or of those of the hand, since the angles which the mutu- 

 ally form in these conditions are scarcely equal to a quadrant aud 

 a half, or 135 degrees. And this fact, which the appearauce of 

 the articular surfaces alone would lead us to suspect, may be 

 reduced to a certainty by the very simple experiment of hending 

 the forearm, and then from extreme supination pronating the wrist, 

 and comparing the lines formed by its anterior surface in both 

 these positions with each other, so as to take the angle through 

 which the surface has passed. Or better still, since it reiuoves all 

 suspicion of interference with the musclee that etfect pronation. fix 



