1909.] 



Innervation of Antagonistic Muscles. 



259 



{e.g. semifendinosus) of that joint being suitably isolated, the myograph can be 

 arranged to register simultaneously the state of contraction or relaxation of 

 both muscles. If, then, excitatory and inhibitory afferents for each of these 

 muscles be stimulated concurrently, summation of the opposed influences of 

 the antagonistic nerves is found to be exhibited concurrently by both 

 muscles. The results of double (excitatory together with inhibitory) 

 stimulation on the antagonist muscles can be grouped into cases belonging to 

 three types. Which particular one of these three types occurs in any 

 particular case depends on the relative intensity of the stimulation of the 

 two afferent nerves. In my experiments usually one of the two nerves has 

 been ipselateral, that is, belonging to the limb to which the observed muscles 

 belong ; the other contralateral, that is, belonging to the opposite fellow limb. 

 The ipselateral nerve excites the knee flexor and inhibits the knee extensor 

 (fig. 9a, Obs. I and II). The contralateral nerve excites the knee extensor 

 and inhibits the knee flexor (fig. 9a). 



Under concurrent stimulation of both ipselateral and contralateral nerve 

 one type of result is that the knee flexor contracts and the knee extensor is 

 relaxed apparently fully (fig. 9b, Obs. V ; fig. 11, Obs. I and II). This is the 

 result when the stimulation of the ipselateral afferent is strong and that of 

 contralateral relatively weak, though yet efficient to cause contraction of 

 extensor muscle were not the ipselateral stimulus concurrently at work. 



In a second type of case the result of the concurrent stimulation of the 

 opposed afferents is that knee extensor contracts and knee flexor is relaxed 

 apparently to the full (fig. 5, Obs. IV). For this result the stimulation of 

 the contralateral afferent has to be strong and that of the ipselateral quite 

 weak, though strong enough to relax the extensor and contract the flexor 

 were not the contralateral stimulus in action at the time. 



In combinations belonging to the above two types, one of the antagonist 

 muscles contracts while its opponent, if previously at rest, does not enter into 

 contraction, or, if previously contracting, is thrown out of contraction and 

 relaxed, exhibiting no obvious contraction either to visual inspection or in the 

 myograph record. The result in these two types of instance, although 

 obtained under concurrent stimulation of both afferents, resembles to outward 

 appearance that of stimulation of either the one or the other of the antagonist 

 afferents alone. 



If, however, the relative intensity of stimulation of the two afferent nerves 

 differs less than in the two sets of cases mentioned, the result of the concurrent 

 stimulation of the two nerves falls out differently. In this third type of case 

 the antagonistic muscles, flexor and extensor, both exhibit obvious contraction 

 concurrently (fig. 9, Obs. II and IV ; and fig. 10). Thus the Observation II, 



