Heukick, Alorphology of Brain of Bony Blshcs. 349 



the first and third methods maintain. In regions of the 

 neural tube farther caudad there are two sets of commissures, 

 one lying in the dorsal and the other in the ventral wall 

 of the tube. These remain in their primitive form in the 

 cord. 



The question novv^ arises, to w^hat extent the same rela- 

 tions persist in the cerebrum. In fishes, since the cortex is 

 anatomically absent and simply morphologically represented 

 by the pallium, it is obvious that the cells and commissures 

 are either absent entirely or represented functionally by 

 structures in other parts of the primary prosencephalic 

 vesicle. Theoretical considerations, as well as such evidence 

 as we have from embryology, show that the tendency of de- 

 velopment in the cerebrum proper is dorso-caudad, i.e., the 

 outgrowths of the primitive vesicle are reflexed and tend to 

 overlap the axial portions caudad. This is also the case to a 

 certain extent even in the growth of the pallial sac in fishes, 

 but since the latter does not contain nervous elements, such 

 revolution cannot change the position of the commissures, 

 etc., belonging properly to the roof Following this clue as 

 given in a previous article, (') it has been possible to deter- 

 mine the relations of all the important tracts, commissures, 

 and niduli of the cerebrum, including testhesodic and kine- 

 sodic niduli, corpus callosum, fornix, hippocampal commis- 

 sure, fornix body, and hippocampus, in an unexpectedly 

 simple way. When we remember that the cortex of higher 

 vertebrates contains those centres whose functions associate 

 them most closely with conscious acts, and that it is regarded 

 as the true organ of consciousness, including all the higher 

 faculties, it becomes of great interest to discover whether the 

 axial lobe of fishes contains cell clusters which can be looked 

 upon as the physiological equivalent of the cortical areas of 

 higher animals. 



The writer, in a series of publications covering most of 



I C. L. Herrick, "Topography and Histology of Certain Ganoid Fishes," Journal 

 OF Comparative Neurology, Vol. I, p. 167, June, 1891. 



