MORPHOGENESIS OF THE CHOROID PLEXUSES 



523 



model is, consequently to the left. The paraphysis which 

 had been removed is represented by a line of white dashes. 

 Figure 24 looks at the same foramen from the lateral side. The 

 model is therefore reversed and the cephalic end points to the 

 right. 



The condition of the roof-plate is diagrammatically represented 

 in figure 12. The differentiation between hemisphere wall and 



Fip;. IG Transverse section from the forebrain of an embryo of Chrysemys 

 marginata having a carapace 8.6 mm. in length. Embryo 5 b, slide 13, sect. 11. 

 X 33 J. 



Fig. 17 Transverse section of the same embryo; section IG, slide 13. X 33J. 



roof plate is clear and the taenia fornicis obvious (figs. 10 and 

 17). The anterior extremit}' of the lateral telencephalic plexus 

 arises plainly from the telencephalic roof plate lateral to the 

 paraphysis and medial to the taenia fornicis (fig. IG). Figure 



17 shows a section posterior to figure 16 through the main body 

 of the plexus, the plexus still b'ing in the roof plate. Figure 



18 is of a section still farther posteriorly. The plexus is here 

 shown crossing the taenia fornicis into the medial hemisphere 

 wall. The taenia fornicis is now medial to the plexus and drop- 



