398 THE SENSORIAL FUNCTIONS. 



na.* Experiments and pathological observations, however, 

 seem to show that the hemispheres of the brain are the chief 

 instruments by which the intellectual operations are carried 

 on; that the central parts, such as the optic lobes and the 

 medulla oblongata, are those principally concerned in sen- 

 sation; and that the cerebellum is the chief sensorial agent 

 in voluntary motion. 



4. Comparative Physiology of Perception. 



OF the perceptions of the lower animals, and of the laws 

 which they obey, our knowledge must, of necessity, be ex- 

 tremely imperfect, since it must be derived from a compari- 

 son with the results of our own sensitive powers, which 

 may differ very essentially from those of the subjects of our 

 observation. The same kind of organ which, in ourselves, 

 conveys certain definite feelings, may, when modified in 

 other animals, be the source of very different kinds of sen- 

 sations and perceptions, of which our minds have not the 

 power to form any adequate conception. Many of the 

 qualities of surrounding bodies, which escape our more ob- 

 tuse senses, may be distinctly perceived, in all their grada- 

 tions, by particular tribes of animals, furnished with more 

 delicate organs. Many quadrupeds and birds possess pow- 

 ers of vision incomparably more extensive than our own; in 

 acuteness of hearing, we are excelled by a great number of 

 animals, and in delicacy of taste and smell, there are few 

 quadrupeds which do not far surpass us. The organ of 

 smell, in particular, is often spread over a vast extent of sur- 

 face, in a cavity occupying the greatest part of the head; 

 so that the perceptions of this sense must be infinitely diver- 

 sified. 



* For a summary of the doctrines of Drs. Gall and Spurzheim, I beg leave 

 to refer the reader to an account which I drew, up, many years ago, for the 

 Encyclopaedia Britannica, and which composed the article "CRANIOSCOPY" 

 n the last supplement to that work, edited by Mr. Napier. 



