84 



THE 



PRINCIPLES OF MVODVXAMICS. 



(4.) The special ab-ductors of the hand — that 

 is, the tiuo carpo-radial extensors— have large 

 retentive components : — 



So that the radio-humeral joint will be in a 

 comparative condition of conservatism. 



73. When the radius is completeh- flexed : 

 (I.) The greater parts of the forces of the 



biceps brachii and of the brachialis anticus Vvill 

 be displacing components. 



(2.) But these displacing components will be 

 antagonized by parts of the forces of the supi- 

 nator longus, the supinator brevis, the special 

 abductors of the hand, and other muscles that 

 span the elbow-joint and have their origin on 

 the lower end of the humerus. In this respect, 

 the radio -humeral joint is in a conservative 

 relation ; and the ulno-humeral joint has con- 

 servative myodynamic relations in any position 

 of the fore-arm except one- — namely, 



74. When the fore-arm is flexed about 2 5 

 degrees. The co-operation of a resisting force 

 against the palm of the hand and the displacing 

 components of the muscles enumerated below 

 will dislocate the ulna and the radius : — 



