EXPLANATION OF THE NERVOUS HAND. 167 



spending to. the "nervous hand," and thus that 

 posture is mechanically brought about. 



3. The nerve-mechanism corresponding to the 

 hand falls spontaneously into the condition corre- 

 sponding to the " nervous hand " when the man is 

 tired or weak. 



4. When the hand of a weak man is held out 

 free, its nerve-mechanism spontaneously places it in 

 the " nervous posture." 



The attempt at explanation may be made again, 

 commencing with the principle of analysis and then 

 applying the principle of analogy. 



Anatomical analysis shows that this " nervous 

 hand " presents two principal elementary conditions : 



(1) Flexion or drooping of the wrist. 



(2) Hyper-extension of the metacarpo-phalangeal 

 (small) joints. 



So much for analysis, now as to analogy. 



Looking for analogy between postures, flexion or 

 drooping of the wrist may be seen, as in a hand 

 that is resting, in a hand that is passively held out 

 while the patient is deeply asleep, or in deep coma, 

 or in a paralyzed arm. It is probable, then, that the 

 wrist flexion indicates the weakness of the " nervous 

 hand." 



Hyper-extension of the metacarpo-phalangeal 

 joints and thumb may be seen as a temporary con- 

 dition in subsultus tendinum and in chorea. In all 

 these cases the unstable condition of the nerve- 

 mechanism is indicated by the extensor movements 

 of small parts. 



Now, looking at the elementary conditions shown 



