530 'Journal of Comparative Neurology and Psychology. 



thalamus requires new definition both toward the thalamus and toward 

 the telencephalon. The latter is furnished in the new facts brought 

 out in this paper; the proper boundary between thalamus and 

 hypothalamus can be determined only after we have fuller knowledge 

 of the internal structure. The metathalamus and thalamus each pre- 

 sents morphological unity and cannot well be improved upon at 

 present. The chief changes needed in the BISTA at present are such 

 as are required by the new facts regarding the telencephalon and the 

 boundary between it and the diencephalon. These will be indicated 

 below. 



ch.op. 



Fig. 45. A, transverse section of the telencephalon of Petroiuyzon. 



Transverse Section of the Telencephalon. — A true transverse sec- 

 tion of any part of the central neiwous system must cut across both 

 dorsal and ventral zones of the neural tube and must cut roof plate 

 and floor plate as nearly as possible at the same antero-posterior 

 level. A little reflection will show that while such a section is readily 

 obtained in any of the lower segments of the brain and cord, a true 

 transverse section is seldom cut in the telencephalon. Such a section 



