Johnston, Forrbrain Vesicle in Vertebrates. 



511 



adult the chorioid fissure is found at the bottom of the very deep 

 groove between the hemispheres and the brain stem and that the 

 boundary between diencephalon and telencephalon runs just along 

 the posterior (thalamic) border of the fissure. These relations are 

 clearly set forth by G. Elliot Smith in a recent paper (1908) on the 

 forebrain of Lepidosiren, which agrees in essentials with that of 

 mammals. 



Fig. 44. Sketch of the human braiu for comparison with Fig. 43. 



When the internal structure of the brain is taken into account it 

 is seen that the boundary line indicated by the development separates 

 centers of different significance. Before it lie the primary and sec- 

 ondary olfactory centers, behind it in the nucleus habenulse and 

 inferior lobes (tuber cinereum) lie the tertiary olfactory centers with 

 reflex functions. This is not true of the boundary line laid down by 

 His which placed the region of the infundibulum (pars optica 

 hypothalami)' in the telencephalon. His was apparently not followed 



