LECTURE IV. 95 



nates nervous activity, whilst the wliite substance acts as a con- 

 ductor. All the fibres of the white substance, all the nerves 

 entering the brain, terminate in the grey ganglia and masses 

 scattered in the centre of the brain or on its surface. It fol- 

 lows, then, that in the question of the relation of cerebral struc- 

 ture to mental development, the grey substance and the parts 

 chiefly composed of it, demand our special attention. 



Now it does not admit of a doubt that many of the grey 

 nuclei in the interior of the brain, are not, strictly speaking, 

 connected with the mental functions, but only with the organs 

 of sense. Just as in the spinal cord the grey matter has different 

 functions, one mass presiding over sensation and another over 

 motion, so are there in the brain grey nuclei whose relation to 

 particular functions can be determined. In that part of the 

 spinal cord which enters the cranium by the occipital foramen, 

 and is then called the medulla oblongata, there are situated 

 the grey nuclei which preside over the respiratory and the 

 cardiac movements ; more in front are other parts which have 

 been experimentally proved to be related to the movements of 

 the body and to the organs of sense. These parts are in our 

 investigations only so far interesting in that the senses may be 

 more developed in some races than in others. Although, how- 

 ever, the acuteness of the senses in some savage tribes excites 

 our astonishment, it appears to be rather the result of train- 

 ing than of an original endowment, since individuals belonging 

 to civilised races, whose calling as hunters or mariners requires 

 constant practice, soon acquire the same acuteness of per- 

 ception. 



On examining a human brain at the base, we see in the 

 centre a nearly white mass ascending through the large occip- 

 ital aperture, which must be divided in order to remove the 

 brain from the cranium. This is the medulla oblongata, in the 

 interior of which we see several grey ganglia, and from the 

 edges of which issue several cerebral nerves, as the vagus 

 which proceeds to the heart, the lungs, and stomach. In front 

 it is continued in a bridge-shaped structure termed the pons 

 Varolii, composed of transverse fibres, and from which emerge 

 fasciae of white matter, which, entering the hemispheres, are 



