. Journal of comparative neurology. sarises plainly from the telencephalic roof plate lateral to theparaphysis and medial to the taenia fornicis (fig. IG). Figure 17 shows a section posterior to figure 16 through the main bodyof the plexus, the plexus still bing in the roof plate. Figure 18 is of a section still farther posteriorly. The plexus is hereshown crossing the taenia fornicis into the medial hemispherewall. The taenia fornicis is now medial to the plexus and drop- 524 PERCIVAL BAILEY ping down to meet the anterior nucleus of the thalamus, whichit does in a few sections and becomes con
. Journal of comparative neurology. sarises plainly from the telencephalic roof plate lateral to theparaphysis and medial to the taenia fornicis (fig. IG). Figure 17 shows a section posterior to figure 16 through the main bodyof the plexus, the plexus still bing in the roof plate. Figure 18 is of a section still farther posteriorly. The plexus is hereshown crossing the taenia fornicis into the medial hemispherewall. The taenia fornicis is now medial to the plexus and drop- 524 PERCIVAL BAILEY ping down to meet the anterior nucleus of the thalamus, whichit does in a few sections and becomes continuous with the taeniathalami. In figure 19, much farther posteriorly, the taeniathalami is present, the plexus being entirely in the medial hemi-sphere wall. The portion of the plexus arising from the medialhemisphere wall is very poorly developed (fig. 19) but its area ofinvagination is extensive (fig. 24). In later stages this posterior part of the plexus develops morerapidly and overshadows the other. Figure 25 shows a lateral. Fig. 18 Transverse section of the same embryo as figure 16. Slide 13, sec-tion 22. X 33J. Fig. 19 Transverse section of the same embryo; section 5, slide 14. X 33|. view of the region around the foramen of Monro in an embryowith a carapace of mm. A pen sketch of the entire modelis appended (fig. 27) showing the region represen ed in figure25. (Figure 24 is of a homologous region in a younger embryo.),The fissura chorioidea appears merely as a big hole in the medialhemisphere wall; all the landmarks are lost. In still later stages,this hole becomes reduced to a long narrow slit. The development of the plexus in size and shape is so welldiscussed and figured by Warren (11) that it will not be con-sidered here. MORPHOGENESIS OF THE CHOROID PLEXUSES 525 DISCUSSION From the foregoing history and description, and from ananalysis of the remaining hterature, for in the history are in-cluded only the most important papers and especially thosedeaUng with
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