340 Prof. C. S. Sherrington. On Reciprocal [Mar. 9, 



nemius occurs. If the nerves of tibialis anticus and extensor longus digitorum 

 have not been severed, though their tendons at the ankle have been cut in 

 order to prevent their mechanical action at that joint, reflex contraction of 

 tibialis anticus, and, to a less extent, in my experience, of extensor longus 

 digitorum, can, by inspection, easily be seen to accompany the reflex relaxation 

 of the unparalysed part of the gastrocnemius. The inhibition can be demon- 

 strated well by producing from the plantar nerve of the opposite leg a reflex 

 contraction of the gastrocnemius just prior to exciting the reflex inhibition 

 from its own nerve. The inhibition can also be demonstrated under 

 decerebrate rigidity. The experiment can be varied by severing the nerve of 

 the outer instead of the inner head of the gastrocnemius and keeping that of 

 the inner head intact for revealing the effect on the muscle. The result is 

 similar in the two cases. The nerve of soleus exhibits a similar reflex; so 

 also in the fore limb do the nerves of anconeus,' supraspinatus, and parts of 

 deltoid and triceps brachii respectively. These likewise, while causing 

 inhibitory relaxation of their own muscles, cause also reflex contraction in 

 their antagonistic muscles, which flex respectively the elbow and the shoulder 

 joints. 



III. Among afferent nerves proceeding from the muscles of the limbs, there 

 are, therefore, as regards their reflex effects upon the musculature, two groups. 

 Both of these evoke reciprocal innervation in antagonistic pairs of muscles; 

 but one group evokes a reflex which excites that muscle from which the afferent 

 nerve itself proceeds and concurrently inhibits the antagonistic muscles, while 

 the other group evokes a reflex which relaxes the muscle from which the 

 afferent nerve proceeds and concurrently excites the antagonistic muscles. 



In both cases the reflex inhibition is not confined to one single muscle, but 

 involves a number of muscles, just as the reflex contraction is not confined to 

 one single muscle, but involves a number. Thus, with the inhibition of 

 gastrocnemius, there can be seen to be associated, in one and the same reflex, 

 reflex relaxation of soleus, crureus, vastus lateralis, and vastus medialis. 

 Similarly, with the reflex contraction of tibialis anticus there can be seen to 

 occur concurrent contraction, more or less pronounced, in extensor longus 

 digitorum, peroneus longus, biceps cruris (posterior part), semi-tendinosus, 

 sartorius, tensor fascia femoris, gracilis, psoas, iliacus, and psoas parvus. It is 

 obvious, therefore, that the reflex inhibition is distributed over a group of 

 synergic muscles, and that, similarly, the reflex contraction is distributed 

 over another group of synergic muscles. The former are extensors of the 

 ankle, knee, and hip ; the latter are flexors of the ankle, knee, and hip. 



In view of the synergic relation apparent in the muscles over which the reflex 

 relaxation is distributed, it might be expected that stimulation of the afferent 



