1912.] Innervation and Symmstrical Muscles. 



227 



them, although it can bring about, it is true, the exhibition of some degree of 

 contraction by both the antagonists at the same time. 



Tbe difference in intensity of reflex influence exerted on the ipsilateral and 

 contralateral limbs respectively may have its biological meaning in the 

 opportunity thus given for the limbs to exhibit either symmetrical reflex 

 movements, or movements of opposed direction right and left, according as 

 there is equality or inequality between their right and left stimuli. 



V. Symmetrical Rebounds. 



It will be noted that in the above attempt to change by experimental 

 means the reciprocal innervation of the symmetrical muscle-pair consisting 

 of right and left knee- extensor into identical innervation, success is reached 

 as regards " immediate "* reflex effect only in so far as identical inhibitory 

 relaxation of the two. Simultaneous contraction of the two in response to 

 concurrent stimulation occurs occasionally with weak stimuli, especially 

 where one of the nerves tends to give ipsilateral contraction. The identical 

 contraction of the two which ensues, however, after their concomitant 

 relaxation is, so to say, not an immediate but a " terminal "f reflex result, 

 for it is due to post-inhibitory rebound. 



Eebound contraction in one muscle of an antagonistic or of a symmetrical 

 pair is so commonly associated with concomitant relaxation of the fellow 

 muscle (tig. 8) of the pair that large identical rebound contractions 



Fig. 8. — Extensor muscles, vastocrurei, of right and left knees. Stimulation of right 

 peroneal nerve. The post-inhibitory rebound of the ipsilateral extensor is 

 synchronous and reciprocal with the post-excitatory relaxation of the contralateral 

 extensor. Decerebrate cat. 



* Gf. T. Graham Brown, 'Quart. Journ. Exp. Physiol.,' 1912, vol. 5, p. 237. 

 t Gf. T. Graham Brown, ' Quart. Journ. Exp. Physiol.,' 1911, vol. 4, p. 331. 



