212 



D. DAVIDSON BLACK 



The roof, which is made up of ependyma, pia and fibrous tis- 

 sue fused together, is everywhere quite thin. Its relations to 

 the thickened base are best brought out in the diagrams (figs. 

 11, 12 and 13). These represent respectively a sagittal and two 

 transverse sections of the brain. 



Vent J. 



12 



Vent.l. 



Fig. 12 Coronal section through fore-part of cerebral vesicle. Vent.l., cav- 

 ity of cerebral vesicle; X., marks point of attachment of thin roof to inner pillar 

 of thickened recurved cerebral margin. X f . 



Fig. 13 Coronal section through mid-part of cerebral vesicle. Rdg., ridge in 

 ventricular cavity corresponding to external furrow (Bas.F.). The relations of 

 this ridge and furrow are further illustrated in figures 50 and 51. Other letters 

 as in figure 12. X f . 



It will be seen in these diagrams that the thickened basal por- 

 tion of the cerebral vesicle presents an arched margin, and the 

 roof is not attached to the apex of this arch but to the base of 

 the inner pillar. This recurved margin subsequently has been 

 identified as a modified hippocampal formation. Thus the point 

 of attachment of the thin roof will represent the fimbria. 



