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 opinions 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 Varolii, and medulla oblongata. SIMMERING 

 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 GALL and SruRZHEiM, 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 is 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 WALKER *, 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 

 the nerves 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. 



