402 J. B. JOHNSTON . 
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39 
Figs. 38 and 39 Two drawings of a clay model made to represent a simplified 
selachian forebrain. From Johnston ’11 a. Figure 38 shows the medial surface, 
figure 39 the rostral surface. The broken line on these surfaces represents the 
medial zona limitans hippocampi. It extends from the neuroporic recess through 
the interventricular foramen along the medial wall of the hemisphere. Compare 
the figures of sections in the paper referred to. This zona limitans is homologous 
with the line of separation of the primordium hippocampi and medial olfactory 
nucleus rostral to the foramen in cyclostomes. See figures 3, 5 and 6. In figure 
38, s.M. marks the continuity of the sulcus limitans hippocampi with the sulcus 
hypothalamicus, very much as in Lampetra and Ichthyomyzon. Compare figure 
41. 
