92 



PEUCIVAL BAILEY 



collection of Dr. ¥. \\. Lillie. In the embryo under consideration 

 toward the anterior end of this region (fig. 7, t.r-p.) the morphol- 

 ogy is somewhat different from that shown in figure 6. In the 

 mid-line again, the nuclei are evenly distributed from ependymal 

 to pial surface and are very numerous. Immediately on either 

 side, however, the wall is greatly thickened in such manner that, 



Fig. 5 Sectionthrough tela chonoideatelencephalimedii of the 28 mm. embryo, 

 H91. X 50. Slide 28, Sect. 362. 



Fig. 6 Section through roof plate of telencephalon medium of the 28 mm. 

 embryo, H 91. X 50. Slide 29, Sect. 367. 



although the pial surface still forms a regular curve, the ependy- 

 mal surface shows a deep notch in the mid-line. The outline 

 of the ependymal surface is again indefinite owing to the loosely 

 arranged cells. The marginal layer approaches almost to the 

 midline. At the extreme anterior end of this region the notch 

 disappears; the ependymal outline becomes definite; and the 

 roof plate thickens markedly in an undoubted lamina terminalis 

 ffig. 20, l.L). 



