258 THE GROWTH OK THE BRAIN. 



fibres (see Fig. 61). The relations of the fibre bundles 

 in the capsule are sometimes so described as to leave 

 the impression that this is the sole portion of the capsule 

 in which such afferent fibres occur. More probably, 

 however, they are distributed through its entire extent 

 because the method of distribution in the cortex, like 

 that for the spinal cord, is such that the fibres bringing 

 afferent impulses terminate in the neighbourhood of 

 cell-bodies whose neurons control the centres for the 

 related muscles, and further, because the general group- 

 ing of the fibres in the internal capsule itself is in the 

 main similar to the grouping in the cortex. The distri- 

 bution of the incoming fibres is consequently such that 

 a large portion of the cortex must receive them, and, 

 judging from its reactions to stimuli, an equally large 

 region must contain cells giving rise to outgoing 

 impulses. The same reactions which lead to the con- 

 clusion that the incoming impulses are brought to the 

 surface of the cerebrum lead also to the conclusion that 

 at this point they pass from one set of nerve cells to 

 another, and that this second set discharges towards the 

 lower lying centres. Thus there is indicated an 

 arrangement by which at the cortex the direction of 

 the nervous impulse is exactly reversed. Such changes 

 of direction may occur in any centre, but the peculiarity 

 of the cortex from the standpoint of physiology consists 

 in the extension over a broad surface of these turning- 

 points for the nerve impulses, an extension which par- 

 ticularly adapts the cortex for experimental study. 

 Granting these points, it is not surprising to find that in 

 a certain sense the entire cortex, so far as it responds 

 directly, is motor, so that the stimulation of it at 

 different points will give rise to muscular contractions. 

 This close association of the two groups of elements 

 brings it to pass also that in the case of the regions 



