THE PRINCIPLES OF MYODYNAMICS. 65 



sions as before, be flexed, and lift a weight of 

 5o Pounds. Then we shall have two equations : 



P=4XW=200 . . . . (i.) 



F=P-W==:i5o .... (2.) 



(i.) The force of the contracting muscles 

 equals 200 pounds. 



(2.) The pressure of the carpus on the base 

 of the radius equals i5o pounds. 



49. The myodynamic relations of the wrist- 

 joint are conservative — even on the application 

 of considerable external force : — 



(i.) The hand is very rarely dislocated : 



(2.) The base of the radius is frequently 

 broken : 



(3.) These conclusions agree with the practical 

 observations of surgeons. — 



Examples: — In Figs. 18 and 19, H=the 

 hand ; C=the carpus ; R a=the radius ; U=the 

 ulna ; f-a=the fore-arm ; f-m=the flexors on 

 the fore -arm ; e-m=the extensors on the fore- 

 arm ; f-c-R=the flexor carpi radialis ; P 0= 

 the plane of the base of the radius ; R=a 

 retentive component ; and d=a displacing com- 

 ponent : Fig. 18 is an outside view of the 



