756 



OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



vesicular matter in an organ of sense, which we have seen that it is ( 753), 

 and if the same kind of change may be excited in the Sensorial Centres by 

 an impression from each source, which has been shown to be a matter of common 

 occurrence ( 758) it can scarcely be deemed unlikely that the Sensorial Centres 

 should be the seat of consciousness, not merely of the impressions transmitted 



Fig. 195. 



Diagram of the mutual relations of the principal Encephalic centres as shown in a vertical section : A, 

 Cerebrum ; B, Cerebellum ; c, Sensori-motor tract, including the Olfactive ganglion olf, the Optic opt, and the 

 Auditory aud, with the Thalami Optici thai, and the Corpora Striata cs; D, Medulla Oblongata; E, Spinal 

 Cord: a, olfactive nerve; ft, optic; c, auditory; d, pneumogastric ; e, hypoglossal; /, spinal: fibres of the 

 medullary substance of the cerebrum are shown, connecting its ganglionic surface with the sensori-motor 

 tract. 



to them by the nerves of the external senses, but also of the impressions brought 

 to them by the " nerves of the internal senses ;" as the sagacious Keil desig- 

 nated the radiating fibres of the Cerebral Hemispheres. And there is on the 

 other hand an d priori improbability that there should be two seats of conscious- 

 ness, so far removed from one another as the Sensory Ganglia and the vesicular 

 surface of the Hemispheres (for to their medullary substance no such attribute 

 can be assigned with the least probability) ; an idea which is quite at variance 

 with that very simple and familiar class of phenomena which consists in the 

 recollection of sensations. For the remembered sensation is so completely 

 the repetition of the original, that we can hardly suppose the seat of the two 

 to be different ; yet the act of recollection is clearly Intellectual, and therefore 

 Cerebral ; consequently if we admit that the Sensory Ganglia are the seat of the 

 original sensation, we can scarcely but admit that they are also the seat of that 

 which is reproduced by a Cerebral act a view which is fully confirmed by the 



1 It is interesting to observe how remarkably this view is confirmed by the history of 

 Development. For the Retina, like the cortical substance of the Cerebrum, is a vesicular 

 expansion originally detached from the Sensory Ganglia, and gradually carried to a greater 

 and greater distance from them ; but still remaining connected by the commissural tract 

 of white fibres, which we call in the one case the Optic Nerve, and in the other the Me- 

 dullary substance of the Hemispheres. 



