534 THE NERVOUS SYSTEM. 



vertical section of a convolution generally presents the 

 appearance of three layers of grey with two intervening 

 layers of white substance, a grey layer being most ex- 

 ternal. In these grey layers, the outer is formed prin- 

 cipally of granular matter and nuclei, like those of nerve 

 corpuscles ; in the deeper layer are more perfectly formed 

 cells. 



It is nearly certain that the cerebral hemispheres are 

 the organ by which, ist, we perceive those clear and 

 more impressive sensations which we can retain, and 

 according to which we can judge ; zndly, by which are 

 performed those acts of will, each of which requires a 

 deliberate, however quick, determination ; pretty, they are 

 the means of retaining impressions of sensible things, and 

 reproducing them in subjective sensations and ideas; 

 4thfy, they are the medium of the higher emotions and 

 feelings, and of the faculties of judgment, understanding, 

 memory, reflection, induction, and imagination, and others 

 of the like class. 



The evidences that the cerebral hemispheres have the 

 functions indicated above, are chiefly these : i . That any 

 severe injury of them, such as a general concussion, or 

 sudden pressure by apoplexy, may instantly deprive a 

 man of all power of manifesting externally any mental 

 faculty. 2. That in the same general proportion as the 

 higher sensuous mental faculties are developed in the ver- 

 tebrate animals, and in man at different ages, the more 

 is the size of the cerebral hemispheres developed in com- 

 parison with the rest of the cerebro- spinal system. 3. That 

 no other part of the nervous system bears a corresponding 

 proportion to the development of the mental faculties. 

 4. That congenital and other morbid defects of the cerebral 

 hemispheres are, in general, accompanied with correspond- 

 ing deficiency in the range or power of the intellectual 

 faculties and the higher instincts. 



[Respecting the mode in which the brain discharges its 



