NERVOUS SYSTEM. 153 
1. The Brain.—That the brain is the organ to which 
the impressions produced by external objects are conveyed, 
and from which the excitements to motion in the different 
parts are propagated, has been demonstrated by observa- 
tion and experiment. We have already stated the com- 
plicated structure of this organ, and the variety in the tex- 
ture and situation of its different parts. What, then, are 
the uses of each? Physiologists have always been greatly 
divided in their opmions on this important subject. 
Some, supposing that the seat of the intellectual opera- 
tions must exist near the centre of the brain, have consider- 
ed the pineal gland as the common sensorium. Others have 
bestowed the same honour on the corpus callosum, corpora 
striata, pons Varolu, and medulla oblongata. SamMERrine 
considers the aqueous fluid, with which the ventricles of 
the brain are, in general, in part filled, as the common cen- 
tre of sensation. According to Gatti and SpurzHeEiM, the 
various operations of sensation and volition, are performed 
in particular parts of the brain, every faculty or feeling ha- 
ving a distinct organ in which it 1s generated. The fore part 
of the brain, they consider as subservient to intellect ; the 
middle to sentiments, and the back part to propensities. Ac- 
cording to Mr Wa ker *, the cerebrum is the organ of 
sensation, or the centre to which all the impressions are 
communicated, and in which deliberation is practised, 
while the cerebellum is the organ of volition. The nerves 
which terminate in the cerebrum, and the anterior columns 
of the spinal marrow, convey impressions to the mind ; and 
themerves which arise from the cerebellum and the poste- 
rior columns of the spinal marrow, execute the purposes of 
volition. 

* Annals of Phil, vol. vi. p. 26. 
