1907.] Innervation of Antagonistic Muscles. 339 



This reflex relaxation of gastrocnemius resembles that produced in the 

 extensor muscles of the knee by stimulation of the proximal end of a 

 cutaneous branch of the crural nerve. If, instead of the cutaneous branch of 

 the peroneal nerve, the branch of the peroneal to the tibialis anticus muscle 

 is severed, and then stimulated proximal to the section, other conditions 

 remaining as above, the gastrocnemius similarly relaxes. In this case, 

 therefore, stimulation of afferent nerve-fibres from the flexor muscle of the 

 ankle evokes reflex relaxation of the extensor muscle of that joint. The 

 case resembles, therefore, the reflex relaxation of the extensor of the knee 

 evoked by stimulating the afferent fibres of the nerve of the flexor muscle of 

 the knee.* 



Let the conditions of experiment remain still as above except that the 

 nerve of extensor longus digitorum is left unsevered, and let the tendons of 

 that muscle at the ankle be severed to prevent their acting on the ankle 

 joint. The extensor longus digitorum is seen to contract at the time when the 

 gastrocnemius relaxes in the reflex excited from the central end of the nerve 

 of tibialis anticus. And, conversely, stimulation of the central end of the 

 nerve of extensor longus digitorum causes reflex contraction of tibialis anticus, 

 together with concurrent relaxation of gastrocnemius. 



II. In these instances, as in others previously reported,! stimulation of 

 afferent nerve-fibres issuing from a muscle excites reflex contraction in that 

 muscle and in muscles synergic with it, and, concurrently, causes reflex 

 relaxation of the antagonistic muscles. Such instances are furnished by the 

 nerves of biceps cruris (posterior part), biceps brachii, gracilis, semi-tendinosus, 

 tibialis anticus, extensor longus digitorum, peroneus longus, etc. But it was 

 shown J that if the nerve of the vasto-crureus muscle in the thigh be carefully 

 split and one of its divisions be then severed, the central end of that division, 

 when stimulated, provokes reflex relaxation of the vasto-crureus muscle 

 itself, with concurrent reflex excitation of the antagonists of that muscle. 

 Here the reflex exhibits, as in the other cases, reciprocal innervation of 

 antagonistic muscles, but the case differs from the others in that that muscle 

 whose nerve is stimulated is itself the field for relaxation, while, conversely, 

 its antagonists, instead of being inhibited, contract. I find a parallel case to 

 this is given by the nerve of gastrocnemius. 



If all the nerves of the limb be severed except that of the outer head of 

 gastrocnemius, and if then the central end of the nerve of the inner head of 

 that muscle be stimulated, reflex relaxation of the outer part of the gastroc- 



* ' Eoy. Soc. Proc.,' vol. 52. 

 t 'Eoy. Soc. Proc.,' vol. 52. 

 % ' Eoy. Soc. Proc., 5 vol. 77. 



