AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



lished (1861) the important observation that when the most ventral or the 

 third frontal convolution in the left hemisphere (often designated Broca's con- 

 volution) was thrown out of function, the power of expression by spoken 

 words was lost, and hence the name of " speech-centre " has been applied to 

 this convolution. 



Since this discovery, which links the neurology of the first part of the 



FIG. 196. Lateral view of a human hemisphere, showing the bundles of association fibres (Starr) r 

 A, A, between adjacent gyri ; B, between frontal and occipital areas ; C, between frontal and temporal 

 areas, cingulum ; D, between frontal and temporal areas, fasciculus uncinatus ; E, between occipital and 

 temporal areas, fasciculus longitudinalis inferior ; C, N, caudate nucleus ; O, T, optic thalamus. 



century with that of to-day, and also forms a fundamental observation in the 

 modern doctrine of cerebral physiology, many steps have been taken. 



It was early observed that although in such cases the capacity for spoken 

 language was lost, nevertheless the muscles which were used in the act of 

 phonation were by no means paralyzed. This relation is due probably to the 

 fact that the speech-centre of Broca does not contain cells which connect 

 directly with the lower nuclei controlling the muscles of phouation. 



The interesting observation was also made that in the ordinary person 

 the muscles could not be controlled for phonation from the right hemisphere. 

 Thus the symmetrical portion of the right hemisphere has not the same physi- 

 ological value. 



Besides this lesion, which involves the cortex frontad to the motor region 

 proper, numerous other lesions namely, those which involve the tracts run- 

 ning between the areas of special sensation (vision and hearing, for example), 

 and the motor or expressive region produce corresponding results (see Fig. 

 197). 



An individual in whom the association tracts between the visual and motor 

 areas have been interrupted can, for instance, see an object presented to him in 



