Herrick, MorpJioIogy of Nervous System. ic;^ 



dorsal and mesal walls (pallium of Rabl Riickhard), which 

 were not fully distinguished from the brain membranes. 

 The proplexus, which is quite large, is sufKcient to call 

 attention to this condition. The openings lying beneath the 

 median walls would, according to the useful system since 

 proposed by Prof Wilder, constitute the portiE, and the 

 opening identified above as the porta becomes the opening of 

 the olfactory. With these changes, and remembering that 

 one of the most remarkable incidents of brain development 

 has been the backward revolution of the mantle portion of 

 the cerebrum, all the difficulties disappear, and we seek the 

 commissures of the mantle far cephalad in front of the thin 

 membranous portion, which seems to be homologous, in part 

 at least, with the velum cerebri supporting the proplexus. 



Rabl-Riickhard has the credit of first demonstrating the 

 fact that the prosencephalon of fishes consists of two thick 

 ventral ganglia, which before had been regarded as the 

 hemispheres themselves, while the whole dorsal surface is 

 membranous. 



The most thorough investigation of the ganoid brain is 

 the paper quoted above by (ioronowitsch. Since this may 

 not be universally accessible, a somewhat condensed transla- 

 tion is added of such parts as apply to the present instalment 

 of this paper: 



" Cerehruvi. — The roof of the prosencephalon is mem- 

 branous, and consists of a variously folded epithelial lamina. 

 The roof of the olfactory lobes, however, consists of thick 

 medullary walls. Between the roof of the prosencephalon 

 and the epiphysis there is a broad membranous sac, the cavity 

 of which is distally in wide connection with the cavity of the 

 prosencephalon. The blind end of the sac is directed proxi- 

 mally (cephalad!). The sac, therefore, must be considered 

 as a broad diverticle of the roof of the prosencephalon, 

 springing from a point cephalad to the origin of the epiphy- 

 sis. This may be called, for the sake of brevity, simply the 

 dorsal sac. 



