214 MENTAL AND PHYSICAL EXERCISE. 



they exhibited. The examination has also been exten- 

 ded to the inferior animals, and the same principles have 

 been applied to their skulls, both as to what respects 

 their general form, and the proportionate size of their 

 individual parts, whether indicating a generic, or an 

 individual difference. 



" In estimating the value of these arguments, I shall 

 arrange them in two divisions, as they relate to general 

 considerations of probability, or as they depend more 

 upon particular facts. 



" And with respect to the first point, I think it will be 

 admitted that there is none of them which possesses more 

 than an indirect application to the question in discussion. 

 Admitting that the perfect organization of the brain is 

 a necessary intermedium for the exercise of the mental 

 powers, we may conclude, that every part of this organ 

 must have a necessary connection with the exercise of 

 these powers, as every part of the eye and the ear has 

 a reference to the production of vision and of sound. 

 Inconsequence of our knowledge of the physical laws of 

 light, and the undulations of the air, we are enabled to 

 trace out the mode in which the several parts of the eye, 

 and of the ear co-operate to produce the ultimate effect. 

 Had we the same knowledge of the mode in which the 

 mind operates upon the brain, we should probably have it 

 in our power to detect the same kind of co-operation of 

 all its parts and structures to the production of percep- 

 tion and thought. But on this point we are in total 

 ignorance, and therefore, although we may go so far as 

 to assert, that a perfect brain, in a certain sense, is essen- 

 tial to a perfect mind, we are unable to say in what way 

 it is so. 



" The only anatomical argument which is of so tangi- 

 ble a nature as to allow of any thing approaching to 

 direct deduction, is derived from a consideration of the 

 degree in which an injury of the brain produces a cor- 

 responding injury of the mental powers. Upon this 

 point I have already stated my opinion, and I have only 

 to add, that while the connection is not of that nature 

 which indicates the relation of cause and effect, so I 

 should be still less disposed to allow, that the fact 

 which we possess are of that distinct and direct nature, 



