THE PHYSIOLOGY OF THE BRAIN. 



621 



tegmenta. The soft commissure is mainly gray matter. 

 Finally a large number of associational fibres, as, unite 

 different parts of the cortical substance of the same hemi- 

 sphere. 



The different gray masses on the same side of the forebrain 

 are also united by fibres. They are either so scattered among 

 others that they cannot be tracked out along special tracts of 

 degeneration; or, as is possible, resemble some of the com- 



FI 



i 



FIG 178. Diagram to illustrate cerebral distribution of the fibres proceeding 

 from the tegmentum. For description see text. 



missural fibres uniting upper and lower regions of gray matter 

 in the spinal cord in having nutritive, centres at each end, 

 and therefore not degenerating on either side of a section. In 

 any case very little is known as to their numbers or paths : 

 their existence is indicated by the dotted lines in Figs. 177, 

 178. 



Omitting the associational and the cross commissure fibres 

 and those uniting the corpora striata and optic thalami,. 



