352 



THE BODY AT WORK 



of the middle cerebral artery, which it plugs, causing apoplexy. 

 A larger or smaller number of muscles on the opposite side of 

 the body are paralysed. If the plugging occurs on the left 

 side of the brain, it is accompanied by aphasia ; but only if it 

 occurs on the left side, owing to the fact perhaps the most 



Kitia.es tlie tic 

 centres 



Sme/l 



Cerebellum. 



Spinal cord 



FIG. 25. THE SURFACE OF THE LEFT CEREBRAL HEMISPHERE, CEREBELLUM, AND MEDULLA 



OBLONGATA. 



Sensory areas are enclosed by broken lines ; certain centres in the association-zones are marked 

 by dots. The sensory area of smell is on the inner aspect of the brain ; so also is the area 

 of vision which borders the calcarine and retrocalcarine fissures, and only rarely extends 

 on to the external surface, as shown in the diagram. The sensory area of hearing is largely 

 hidden within the fossa of Sylvius, the opening into which is indicated by the dark line 

 above it. The kinsesthetic-sensory areas for the various muscles of the body occupy 

 the territory between the dotted line in front and the bottom of the fissure of Rolando 

 behind. They do not extend on to the posterior wall of this fissure. It is impossible at 

 present to define the boundaries of any of the centres in the association-zones. 



remarkable in connection with the localization of speech 

 that only on the left side is the cortex trained to utter words. 

 In course of time the patient may recover the power of speaking, 

 but not until he has, with almost as much labour as in child- 

 hood, educated the right side to do the work. There are four 



