Ill 



having interms-liate degrees of development. 



It has seemed to me advisable to distinguish but two col- 

 lections of neurones in the thalamus of Wustelus. One group 

 represents a differentiation of the ancient central gray matter; 

 this I have designated the nucleus strati grisei. The other 

 collection is certainly the one from which the several genic- 

 ulate nuclei of higher vertebrates have been derived; this I 

 have called the nucleus geniculatum. 



a. The nucleus Sti'ati Grisei. — As has just been mention- 

 ed, this collection of neurones represents a differentiation 

 of the primitive central gray matter. The nucleus strati gri- 

 sei has retained its original situation next the third ventri- 

 cle (Big.84,n. s. g. ). It forms a broad zone just within the 

 limitans interna, comprising something like one-fourth the 

 thickness of the entire thalamus. 



The neurones of this group are the largest of the thal- 

 amus. The cell-bo iy has a polygonal form, the several diam- 

 eters not greatly unequal. The dendrites radiate freely in 

 all directions, but they are not very long. The nucleus of 

 the cell has an sccentric position, causing the cytoplasm to 

 appear massed on the side from which the chief dendrites arise. 

 The chromatic substance is disposed in a ten thin strands having 

 thickened nodes. The entire amount of chromatin is not great, 

 and 30 the nucleus presents a lightly stained appearance. The 

 tigroii substance is limited almost entirely to that part of the 



