1893.] Correlation of Action of Antagonistic Muscles. 413 



drawn between them. I find that from this posterior region, as 

 well as from Ferrier's " motor " region, can the tonus of the external 

 rectus be inhibited in the orbit of the same side as the hemisphere 

 stimulated after the 3rd cranial nerve of that side has been cut 

 through. 



An extremely interesting observation has recently been made by 

 Mott and Schafer.* Experimenting together, they have seen that 

 by simultaneous excitation of the frontal cortex of both right and left 

 hemispheres the two eyeballs can be set approximately in the primary 

 position, sometimes with a slight degree of convergence. I have, in 

 two Bonnet Monkeys, repeated this experiment after having pre- 

 viously performed section of both right and left 3rd nerves and both 

 right and left 4th nerves at their origin from the brain. After the 

 section there was considerable double divergent squint, and in one of 

 the experiments the strabismus of the left eye was distinctly the 

 greater in degree. The effect of simultaneous bilateral excitation, 

 approximately balanced, of the frontal cortex was to cause both eyes 

 to be rotated inwards up to, and certainly in some trials beyond, the 

 primary position. ' The double divergent squint was converted into 

 a slight degree of convergence. Here, where the external recti were 

 the only ocular muscles still connected with the central nervous 

 system, convergence must have been due to simultaneous bilateral 

 inhibition of the tonus of the right and left external recti. It is 

 difficult to find any other interpretation for these results than that 

 the excitation of the cerebral cortex, just as it occasionally inhibits 

 the tonus of the muscles of the thumb or hallux, also possesses the 

 power of inhibiting the tonus of ocular muscles, at least of the 

 external straight muscle. Further, it would seem that this inhibitory 

 activity of the cortex is more constantly elicitable experimentally in 

 the case of the muscles of the eyeball than in the case of those of the 

 hand and foot. That the cerebrum nominally exerts a more or less 

 tonic inhibitory influence over the lower local centres subserving 

 muscular tonicity and local muscular reflex action is a widely 

 accepted doctrine. The above observations accord with and, as I 

 think, extend the data for such a belief. 



The above experimental results may, it seems to me, be all of them 

 explained on an hypothesis that the cerebral cortex can inhibit 

 muscular tonus and reduce it even to paralysation limit ; but it does 

 not seem necessary to suppose that the cortex, although it can thus 

 inhibit tonus in striped muscle, can also inhibit the active contraction 

 of it. This second assumption seems necessary, however, to explain 

 the following result. If, after section of both right and left 3rd and 

 right and left 4th nerves, the left frontal cortex be excited and both 

 eyes made to deviate to the right, excitation of the right cortex (the 



* 'Brain,' vol. 17, p. 165. 



