92 



On the Morphology of the Pineal Kegion 



brain, and of two layers of ependyma, of which the posterior is the 

 thinner. 



The plane of Fig. 13 is approximately that of the dotted line B in 

 Fig. 6. The velum, V, belongs to the fore-brain, dividing the cavity 

 thereof into a large anterior (in Fig. 13 lower) chamber and the much 

 smaller chamber of the post-velar arch, which is extended far out lat- 

 erally, the lateral cavities being slit-like; the lateral post-velar slits are 

 bounded in front (below) by a thin ependyma, and posteriorly (above) 

 by the thick brain wall of the tuhercula intermedia in which one readily 



noJi 



Fig. 11. Embryo of 28.0 mm. Transverse series, 232, section 130. The plane of 

 the section is indicated by the dotted line A in Fig. 6. x 30 diams. 



Fig. 12. Embryo of 28.0 mm. Transverse series, 232, section 163. The plane of 

 the section is indicated by the dotted line B in Fig. 6. x 30 diams. 



distinguishes the lateral prolongations, s. c, of the superior commissure. 

 As the tubercula belong to the fore-brain their junction with the mid- 

 brain, which is marked externally by the apex of a deep furrow, indi- 

 cates the division line between the first and second primary cerebral 

 vesicles. From such a section as Fig. 13 one might be easily led to 

 interpret the velum not as the division between the diencephalon and 

 prosencephalon, but between mid- and fore-brain, and further to inter- 

 pret the tubercula as appendages of the mid-brain. Attention should 

 be paid to the two lateral projections, L. cli., of the ependyma on the 



