314 NERVOUS SYSTEM. 



wliicli gives rise to voluntary movements is generated in the 

 brain, and is conveyed by the motor nerves to the appro- 

 priate muscles. We have seen, also, that the centres of the 

 encephalon may be concerned in reflex action. In addition, 

 parts of the brain act as centres of sensation and volition and 

 are concerned in the varied phenomena of intellection. 



The encephalon, or what is ordinarily known as the brain, 

 consists of a number of ganglia, or collections of gray matter, 

 connected with each other, and also, by the different columns 

 of the cord, with the motor and sensory nerves of the gen- 

 eral system. Certain of these ganglia have separate and dis- 

 tinct functions, which are more or less completely understood ; 

 while there are, in addition, masses of gray substance, the 

 physiological relations of which are as yet obscure or entirely 

 unknown. The greatest and the most important of all, the 

 gray matter of the cerebral hemispheres, undoubtedly has 

 subdivisions connected with distinct attributes of the mind ; 

 but our positive knowledge with regard to these divisions is, 

 at the present day, very meagre, though this subject has long 

 been a favorite field for philosophic speculation. 



Confining ourselves strictly to the limits of positive infor- 

 mation, we may recognize the following parts of the encepha- 

 lon as distinct ganglia : 1. The gray matter of the cerebral 

 hemispheres ; 2. The gray matter of the cerebellum ; 3. The 

 olfactory ganglia ; 4. The gray matter of the corpora striata ; 

 5. The gray matter of the optic thalami ; 6. The tubercula 

 quadrigemina ; 7. The gray matter of the tuber annulare, or 

 pons Yarolii ; 8. The ganglion of the medulla oblongata. In 

 addition, the following parts have been made the subject of 

 physiological investigation or speculation, with results more or 

 less definite. The peduncles of the cerebrum and of the cere- 

 bellum ; the pineal gland ; the corpus callosum ; the septum 

 lucidum ; the cerebral ventricles ; and the pituitary body. 

 "We have, however, little if any positive information concern- 

 ing these parts, except their general anatomical relations ; 

 and their physiology really amounts to little more than a 



