348 MESSRS. F. GOTCH AtfD V. HORSLEY 



of one cortex, suggest that the corpus callosum is a true commissure between the 

 excitable or " motor " areas. 



BROWN-SKQUARD* had previously shown that the corpus callosum was excitable 

 about its middle third, and he consequently regarded its fibres as commissural between 

 the hemispheres. 



8. Degeneration of Fibres after Excision of Portions of the Cortex Cerebri. 



The phenomenon of bilaterality of function has also been referred to the normal 

 exercise of those fibres which degenerate bilaterally (PiTREst) in the spinal cord after 

 lesion of one hemisphere. Although the degeneration method has established com- 

 pletely the existence of such atrophy of channels in both lateral columns of the cord 

 consequent upon a unilateral cerebral lesion, we do not, unfortunately, know whether 

 these channels are " recrossed," as suggested by SHERRINGTON,^ CHABCOT, and others, 

 or what is their destination, or whether they are to be regarded as of constant 

 occurrence. As regards the latter point, it is certainly at present considered that 

 they are not constantly affected by a cerebral lesion, and yet more rarely degenerate 

 after a hemisection of the spinal cord. As yet, therefore, the method does not afford 

 anatomical means of deciding the questions at issue. 



RELATION OF THE FOREGOING FACTS TO OUR OWN EXPERIMENTS. 



In summarising the facts thus collated on this subject, it is difficult to avoid discus- 

 sing the theoretical interpretations advanced by the authors quoted, but we do not 

 think that anything is to be gained by such a procedure, and intend now to merely 

 point out what conditions yet remain to be satisfied before anything like a full con- 

 clusion can be arrived at. 



All agree that in the intact nervous system a nerve impulse from one hemisphere 

 may readily pass to the other, excite it, and thus bring about bilaterality of movement 

 as a result. 



Nothing, however, can be judged as to such crossing to the other hemisphere being 

 necessary for bilateral function until it is clearly defined in which part of the body 

 such functional effects occur. 



We must for this reason exclude altogether from the present discussion the 

 facial movements, since these (see p. 344) are in great measure bilaterally repre- 



* ' Compt. Rend. Soc. de Biol.,' 1879, p. 165 ; 1881, p. 204. 

 t 'Archives de Physiologic,' 1884, p. 142. 



J 'Journal of Physiology,' 1885, p. 177. See also summary by TOOTH: " Gulstonian Lectures on 

 Secondary Degenerations of the Spinal Cord," 1889. 

 Of. PANETH ; also UNVERRICHT. 



