112 

 cytoplas'n havi'i^ the Greatest mass. Some of the ti>J,roi'i3 are 

 altogether irregular in form and are relatively quite lart5e. 

 Pig. 62 exhibits t/io neurones as they lie in place. 



The nucleus strati grisei is the terminal station for 

 those axones of the tractus strio-thalamicus having their or- 

 igin in the general striaturn. Tnese sweep into the nucleus 

 in bundles, and their terminations are to be noted bet/»e3n the 

 constituent neurones (Pig. 24, f . s. t. ) . 



The neurones of the nucleus strati grisei are, primarily, 

 a relay in the olf acto-motor chain. The tractus strio-thala- 

 micus terminating here is one of the links of that chain, as we 

 shall point out in detail under Section VIII. The axones from 

 the cells of the nucleus strati grisei pass backward into the 

 base of the midbrain as the tractus thalamo-tectalis, and then 

 sweep upwari into the tectum to lie in the stratum medullare 

 profandum. Here they are associated with other sensory nerve- 

 fibres, as already noted in Section VI, and the entire group 

 becomes related to the remarkable motor conducting path provi- 

 ded by the cells of the roof-nucleus and the fibre of Reissner. 



It is certainly not worth while, with the knowledge which 

 we have at present, to attempt an extensive comparison of the 

 nucleus strati grisei with the specialized thalamic nuclei of 

 higher vertebrates. It seems fairly safe, however, to regard 

 the nucleus rotandus and the nucleus magnocellularis as de- 

 scendents of this simple collection of cells founi in the thal- 

 amus of selachians. 



