334 



APPLIED ANATOMY. 



When rotation of the hand occurs it is accomplished by pronating or supinating 

 the forearm. If the wrist-joint possessed this latter movement it would be a ball- 

 and-socket or enarthrodial joint. The hand can be flexed and extended through an 

 arc of approximately 140 degrees and adducted and abducted about half as much. 

 The position assumed by the bones in flexion and extension is shown in Figs. 343 

 and 344. 



Adduction or bending toward the ulnar side is much greater than is possible 

 toward the radial side. The fact of the ulna not coming so low as the radius 



Scaphoid 



Trapezium / Second metacarpal 

 Trapezoid 



FIG. 343. Position assumed by the carpal bones in flexion of the wrist. 



accounts, at least in part, for this. The lateral ligaments check the movements of 

 abduction and adduction, and in addition the contact of the styloid process of the 

 radius with the trapezium prevents further outward movement. 



The extent of the movements of the wrist of course varies much in different 

 individuals. The laxness of the joints in children, women, and those not accustomed 

 to hard manual labor is well known. 



The movements of the wrist are performed by two different sets of muscles. 



Scaphoid 

 Trapezoid 



Trapezium 



Second metacarpal 

 FIG. 344. Position assumed by the carpal bones in extension of the wrist. 



One set comprises the flexors and extensors of the carpus and the other the flexors 

 and extensors of the thumb and fingers. 



The first set is composed of the flexor carpi radialis and flexor carpi ulnaris, 

 with which we may perhaps include the palmaris longus, although it properly 

 belongs with the finger muscles, and of the extensor carpi ulnaris, extensor carpi 

 radialis longior, and extensor carpi radialis brevior. If the fingers are clinched 

 and the extensors of the fingers contract they aid the three carpal extensors to bend 

 the hand backward. If the fingers are held extended and the flexors of the fingers 

 contract they aid the carpal flexors to bend the hand forward. Contraction of the 



