FUNCTIONS OF THE CEREBRAL HEMISPHERES 503 



Let us see how far experimental evidence bears out this localisa- 

 tion. 



(a) TACTILE AND MOTOR SENSIBILITY. A lesion limited to 

 the ascending frontal convolution may produce paralysis of 

 definite movements or groups of muscles without any detectable 

 interference with sensation. When, however, in man a wide- 

 spread injury, involving both the Rolandic area and the adjacent 

 portions of the brain, occurs as the result of some morbid condition, 

 such as blockage of the middle cerebral artery, the resulting hemi- 

 plegia is almost always associated with a greater or lesser degree of 

 hemiancesthesia. We are therefore justified in locating tactile and 



' Tactile ' area 



Olfactory area 

 FIG. 229. Inner surface of the same hemisphere. (FLECHSIG.) 



muscular sensibility somewhere in the region of the central convolu- 

 tions, and it is probable that while it may include the motor area 

 its chief representation is to be found in the post-central gyrus, i.e. 

 the ascending parietal convolution. 



The sensory aura which precedes an attack of Jacksonian epilepsy 

 points to the motor area itself having some degree of sensory functions, 

 and it has been observed that faradisation of the central convolution 

 in man may produce tingling sensations in the part of the body which 

 is the seat of the muscular contractions induced by stimulation. 

 No pain is, however, felt as a result of the stimulation. The impulses 

 which subserve cutaneous and muscular sensibility travel up to the 

 brain in the mesial fillet. This tract comes to an end in the ventro- 

 lateral portion of the thalamus and the subthalamic region. The 

 new relays of fibres, which carry on impulses to the cortex, arise in 

 the thalamus and pass through the hinder limb of the internal capsule 



