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



sure until they have been thoroughly examined under conditions favourable 

 for the detection of reflex inhibition. It seems not unlikely that they are 

 inhibited in the crossed reflex. 



It would seem therefore that, as said above, the distribution of the reflex 

 effect is in the crossed reflex mainly, if not entirely, to the same muscles as 

 those affected by the uncrossed reflex, but that the incidence of excitation 

 and inhibition upon the motor neurones of those muscles is converse in the 

 two reflexes. Those muscles which undergo reflex relaxation in the idiolateral 

 reflex exhibit reflex contraction in the crossed reflex. In giving the above 

 detailed lists of muscles observed to contract or relax in these reflexes, it is 

 not intended to assert that the reflex throws into or out of contraction no 

 other muscles of the limb. All that is meant is that in the muscles cited the 

 reflex effect mentioned has been regularly observed. 



VI. It seems noteworthy that those muscles, the afferent nerves issuing 

 from which evoke reflex relaxation of those muscles themselves, possess 

 certain physiological characters in common. They are all extensors, extend- 

 ing respectively the knee, the ankle, and the elbow. They are all muscles 

 which, after decerebration of the animal (rabbit, cat, dog, monkey), markedly 

 exhibit decerebrate rigidity. They all are muscles which, in the standing 

 posture and in progression, counteract, by tonic contraction, the effect of 

 gravitation and prevent the limbs yielding under the weight of the body. 

 Two of them certainly yield " jerk-phenomena," e.g., " knee-jerk " and 

 " elbow-jerk." Another among them yields the allied phenomenon, ankle- 

 clonus. They are all muscles for which the toxic agents, strychnine and 

 tetanus-toxin, show marked predilection. They seem, therefore, in these 

 respects to belong to a homogeneous functional group. 



A question naturally arising in regard to these muscles is, whether in 

 the afferent nerves issuing from them there exist no fibres at all which can 

 provoke in them reflex contraction. In my experiments on their nerves the 

 stimulus applied to the nerve trunk has been faradism or mechanical com- 

 pression. It must be remembered that when stimulated in this way the 

 plantar nerves likewise always evoke reflex inhibition in these muscles in 

 the idiolateral hind limb. Yet there is a reflex — the " extensor thrust " * — 

 obtainable from the pi anta (dog), which causes, not relaxation, but contraction 

 of these very muscles ; and this reflex ceases when the plantar nerves are 

 severed. There appear, therefore, to be in the plantar nerves some afferent 

 fibres which can excite reflex contraction of the extensor muscles of the limb, 

 although when the whole of either plantar nerve trunk is excited by faradi- 

 sation or by mechanical compression, the reflex produced is, in my experience, 

 * ' Eoy. Soc. Proc., 5 vol. 66, p. 66 ; also ' Journ. of Physiology/ vol. 30, p. 39. 



