30 THE HUMAN BRAIN. 



themselves room on the hard inside of the skull, and are the most 

 irresistible agents in the human world. 



At a considerable depth the two hemispheres unite together, and 

 below their union, if the cerebrum be opened, we come to certain 

 cavities termed the ventricles of the brain. Of these there are four, 

 all communicating with each other ; and a fifth is enumerated, but 

 of small size, and disconnected from the rest. The four cavities form 

 a continuous chamber, and always contain more or less fluid. Thus 

 the brain, far from being prepared for rest, is constituted internally 

 upon the movable pivot of this fluid cushion of the ventricles. 



The cerebellum lies behind and underneath the cerebrum, of which 

 it is said to be one-eighth the size, and it is divided into lobes and 

 lobules. It consists of gray and white substance, not disposed in 

 convolutions but in thin plates. There is said to be no direct com- 

 munication between the cerebral hemispheres and the cerebellum. 

 The latter is evidently not a revolving, thinking, or spiral organ, but 

 a battery of determination and power : thoughtful consciousness does 

 not connect itself with the back of the head, or with the cerebellum. 

 Its form too, double fisted, does not answer to the cerebral functions. 

 Its visceral or hidden situation also brings it into analogy with the 

 other viscera, in which there is no freedom of thought, but fixed ac- 

 ceptation and permanent action. 



The nervous system, though apparently homogeneous, is con- 

 structed of distinct pieces, which are extraordinarily united, and ex- 

 traordinarily capable of separation in their functions. The first piece 

 is the proper spinal marrow, with all the nerves of the limbs, trunk 

 and head which issue from it. This lowest pillar of the cerebral 

 system is in a manner complete in itself, and receives impressions, 

 and executes actions, on its own account. It consists of a running 

 axis of gray matter of a peculiar form, and in front gives off the nerves 

 that convey bodily motions, at the back receives those which carry 

 bodily sensations. The circle of its operations is therefore as follows. 

 When an impression appeals to it from the body through its quasi- 

 sentient nerves, this mounts to the gray centre to which the nerve 

 carrying the impression belongs : an instant organic determination 

 then occurs in the centre, a decision takes place, and a motion is 

 sent down through the corresponding motor nerve to the parts which 



