THE CEREBRAL HEMISPHERES. 317 



and many of them are still so uncertain and obscure, that 

 they cannot as yet be connected satisfactorily with the exact 

 results of physiological inquiry. All that we can do at pres- 

 ent, is to recognize certain ganglionic masses, the separate 

 functions of which have been more or less accurately de- 

 nned, and show, as far as possible, their anatomical relations 

 to each other and to the cord. 



The separate collections of gray matter concerning which 

 we possess positive physiological knowledge are, the gray 

 matter of the cerebral hemispheres and of the cerebellum, 

 the corpora striata, optic thalami, tuber annulare, or pons, 

 and the medulla oblongata. To these may be added, the 

 olfactory ganglia, which preside over the sense of smell, and 

 the tubercula quadrigemina, or optic lobes, which are the 

 centres connected with vision. The minute anatomy of the 

 nerve-fibres and the nerve-cells, with their mode of connec- 

 tion with each other, have been already considered with suf- 

 ficient minuteness under the head of the general structure 

 of the nervous system. 1 We shall here discuss chiefly the 

 direction of the fibres through which the encephalic ganglia 

 are connected with the periphery, the fibres connecting the 

 different ganglia with each other, and, in the case of the 

 larger ganglia, certain commissural fibres connecting to- 

 gether their different parts. 



In the wealth of literature pertaining to the minute 

 anatomy of the encephalon, it is somewhat difficult to sepa- 

 rate and define the well-established facts which have a direct 

 bearing upon physiology. Perhaps the most elaborate and, 

 to a certain extent, the most satisfactory observations upon 

 the various points to be considered, are those of Luys ; but 

 this author describes the course of the fibres with an exacti- 

 tude that seems hardly justified, in all instances, by the facts, 

 in view of the inevitable difficulty and uncertainty of some 

 of the processes employed ; and the graphic and admirable 

 delineations by which the work is illustrated, though profess- 



1 See Chapter I. 



