186 



Antagonistic Muscles and Reciprocal Innervation. 



should actively contract exactly when another part (that extending 

 the elbow) becomes relaxed is exactly comparable with a phenomenon 

 which has been described by one of us in treating of spinal reflexes, 

 both in the triceps itself and in the quadriceps femoris. And we 

 have similarly seen in the quadriceps femoris, on exciting the cortical 

 region yielding extension of the hip, a relaxation of a part of the 

 quadriceps (a part which flexes the hip) with contraction of another 

 part (which extends the knee). 



We hope, in a longer communication, in which the literature can 

 be dealt with, to give a more detailed account of other instances of 

 co-ordination, in which inhibition of the contraction of the so-called 

 voluntary muscles makes its appearance in result of excitation of the 

 cortex cerebri. The examples cited in the present Note are evidently 

 intimately related to those to which attention has been already called 

 in Second* and Third Notesf on the co-ordination of antagonistic 

 muscles already presented to the Society. 



Addendum. 



Since the above was written, one of us (C. S. S.) has had oppor- 

 tunity to perform further experiments both on the monkey and the 

 cat, and has carried out excitation of the fibres of the internal 

 capsule, as well as excitation of the cortex cerebri. Knowledge is at 

 present completely vague as to which of the many elements in the 

 cortex constitutes the locus of genesis of the reaction obtained by 

 electrical stimuli applied from the cerebral surface. It is therefore 

 conceivable that the elements of the pyramidal tract are only 

 mediately excited by moderate faradisation of the cortex. If so, 

 inhibitory effects produced by excitation of the cortex might likely 

 enough not occur under direct excitation of the cut fibres of the 

 capsula interna. 



As a matter of fact, however, the results obtained from the in- 

 ternal capsule have been as striking as those obtained from the 

 cortex itself. From separate points of the cross-section of the 

 capsula, relaxation of various muscles has been evoked. 



Among the muscles, inhibition of which has been directly observed, 

 are supinator longus, and biceps brachii, the triceps, the deltoid, the 

 extensor cruris, the hamstring group, the flexor muscles of the ankle 

 joint, and the sternomastoid. 



The spots in the cross-section of the capsula which have yielded 

 the inhibitions are constant, that is, the position of each when 

 observed has remained constant throughout the experiment. The 

 area of the capsular cross-section at which the inhibition of the 



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

 f ' Koy. Soc. Proc./ vol. 60. 



