THE FISSURA HIPPOCAMPI Bs) 
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Fig. 20 Outline sketch of the same model as that shown in figure 19. The 
broken lines indicate the position of the sulcus limitans, the most caudal boundary 
of the telencephalic evagination, and the separation of the thalamus from the 
hypothalamus. The extent and the boundaries of the olfactory area projected 
upon the medial wall of the telencephalon can be seen through the main body of 
the thalamus. The planes of figures 47 to 50 are indicated. 
Figs. 21 to 25 A series of transverse sections, pen-and-ink outlines, made 
with the Edinger apparatus, through the various levels of the telencephalon 
of no. 1121, the 11.8-mm. embryo. The numbers below the sections correspond 
to those in figures 8 and 11 and each indicates a specific section. X 50. 
Fig. 21 At the level of the optic evagination. 
Fig.22 Through the middle of the lamina terminalis. 
Fig.23 Through the tela chorioidea telencephali medii. 
Fig. 24 Through the paraphysis. In this and the preceding figure the wall 
of each cerebral hemisphere shows four distinct zones. Beginning in the mid- 
plane they may be designated as follows: 1) A thin septal area, telencephalic 
roof plate; 2) A thicker homogeneous area, the septum ependymale, bounded 
laterally by a shallow ventricular sulcus, the sulcus limitans hippocampi; 3) A 
small area showing a narrow mantle layer emerging from the matrix, the future 
hippocampus; 4) An adjoining and still more lateral area where no clear mantle 
zone is visible, the neopallium. 
