GENERAL SURVEY OF THE STRUCTURE OF THE BRAIN. 369 



that the resistance to conduction in the direction of this axis 

 is smaller than in the nerve-fibre plexus of the grey ganglionic 

 mass, and that upon this depends the circumstance that the 

 isolation of the conduction remains unimpaired. 



An instructive general survey of the leading points in the 

 structure of the brain may be obtained from the examination 

 of transparent sections of the brains of small Mammals, which, 

 with low powers, permit not only the relative size of the 

 several parts, but the general arrangement of the internal 

 structure of the organ, to be followed. 



The nerve cells of the brain are collected into four principal 

 grey masses. 



1. The uppermost mass, in which originates the entire 

 medullary portion of the brain, is the superficial grey matter 

 of the cerebral hemispheres, or cortex of the cerebrum. 



2. The second collection of grey matter is formed by the 

 masses which, since the time of Gall, have been termed the 

 ganglia of the cerebrum (Corpus striatum and Thalamus). 



3. The tubular mass of grey matter, the persistent expression 

 of the original form of the brain, which extends from the tuber 

 cinereum to the conus medullaris of the spinal cord, and lines 

 the internal surface of the central organ as the grey substance 

 of the central cavities. 



4. The grey substance of the cerebellum, which occurs partly 

 as a superficial expansion, and partly in the form of scattered 

 collections of cells, that on the one hand constitute the super- 

 ficial and deeply seated grey masses of the cerebellum itself, 

 and on the other the grey substance of the segments of the 

 cerebral peduncles that are traversed by the medullary sub- 

 stance of the cerebellum. 



In order to construct a schematic representation of the 

 structure of the brain, the most appropriate point of departure 

 appears to be to consider the processes of consciousness as the 

 function of the cerebral hemispheres. Amongst other grounds 

 for this assumption is the circumstance that the collection of all 

 conductors in this morphological unity obviously coincides with 

 the collection and combination of all sensory processes in the 

 consciousness alone. 

 VOL. II. 



'^flST**^ 



