No. 2.] NERVE-MUSCLE EXPERIMENTS. 389 



We thus find that the results of the separate stimulation of 

 the nerves do not harmonize completely with those obtained 

 from stimulation of the entire sciatic, or what is the same 

 thing its two branches simultaneously. The difference is an 

 important one. From simultaneous stimulation of both nerves 

 with low I and R adduction of the toes always results but when 

 high I and R are used abduction always takes its place. Now 

 on the theory proposed by Wedensky the adductor nerve 

 fibers should show themselves more irritable to weak stimuli 

 than to strong and vice versa for the abductor. The same 

 holds true of Bowditch's explanation in which however the seat 

 of the irritibility is not located. But the reverse is the case. 



Any explanation of this phenomenon will have to account 

 for the fact that nerve fibres contained in one trunk, e.g. the 

 peroneal which is supposed to be a pure flexor nerve, can cause 

 flexion of some parts of the limb and extension of other parts. 



Primarily, of course, the vertebrate limb contains two sets 

 of muscles antagonistic to each other, directly and wholly, as 

 in the case of the fish fin, with movement in one plane back- 

 wards and forwards. Secondarily, however, some of these 

 muscles, especially near the end of the limb, become differ- 

 entiated into sets with new functions, e.g. that of controlling 

 the digits. Their nerve supply is derived from the trunk 

 which supplied the primitive arrangement of the parts. In 

 the complicated limbs of all vertebrates above the fishes some 

 muscles, split off from the extensor set, acquire flexor con- 

 nections, or are only used in the flexion of the limb, and 

 vice versa. 



The theory of nerve control proposed by Wedensky calls for 

 a greater sensitiveness to stimuli on the part of the flexor 

 nerves. But from what has been said above it is evident that 

 some nerve fibres of the flexor groups may be so changed that 

 they are sensitive to the stronger stimuli only, and they are 

 called into action only with the extensor group, and vice versa, 

 for the flexor nerves. This change is doubtless more in the 

 nature of a modification of the central cells of origin of the 

 motor fibres than of the fibres themselves. Whatever its 

 nature may be it indicates that Wedensky' s results do not 



