chap, xv.] THE WRIST AND HAND. 253 



end of the radius is very cancellous, while the shaft 

 contains a good deal of compact bone. At about 

 three-quarters of an inch from the articular surface, 

 these two parts of the bone meet, and their very 

 unequal density greatly tends to localise the fracture 

 in this situation. As to the mechanism of this lesion, 

 many different opinions are still held, and a vast 

 deal has been written on the subject. I subjoin Pro- 

 fessor Chiene's account of this lesion, because it may 

 be taken as representing with admirable clearness the 

 views most generally accepted at the present time as 

 to the nature of this injury. Into the discussion itself 

 I do not propose to enter. The deformity in Colles' 

 fracture is entirely due to the displacement of the 

 lower fragment. " The displacement is a triple one : (a) 

 backwards, as regards the antero-posterior diameter of 

 the fore-arm ; (b) rotation backwards of the carpal sur- 

 face on the transverse diameter of the fore-arm ; (c) rota- 

 tion through the arc of a circle, the centre of which is 

 situated at the ulnar attachment of the triangular 

 ligament, the radius of the circle being a line from the 

 ulnar attachment of the triangular ligament to the tip 

 of the styloid process of the radius, (a) When a 

 person in falling puts out his hand to save himself, at 

 the moment the hand reaches the ground the force is 

 received principally by the ball of the thumb, and 

 passes into the carpus, and thence into the lower end 

 of the radius. If, at the moment of impact, the angle 

 between the axis of the fore-arm and ground is less 

 than 60, the line representing the direction of the 

 force passes upwards in front of the axis of the fore- 

 arm ; the whole shock is therefore borne by the lower 

 end of the radius, which is broken off, and, the force 

 being continued, the lower fragment is driven back- 

 wards. When at the moment of impact the angle 

 is greater than 60, the line of the force, instead 

 of passing in front of the axis of the arm, passes up 



