672 C. JUDSON HERRICK AND JEANNETTE B. OBENCHAIN 



Figs. 5 to 12 Comprise series of cross sections through the brain of Ichthyomy- 

 zon at the levels indicated on figure 3. X 36. 



Fig. 5 Section passing through the interventricular foramen and decussation 

 of the optic tracts. 



Fig. 6 Section passing through the primordium hippocampi and lobus subhip- 

 pocampalis a short distance behind the interventricular foramen. The lamina 

 of cells representing the primordial corpus striatum (c.s.) is extensively developed, 

 though for the most part it is withdrawn from the ventricular surface. 



Fig. 7 Section passing through the caudal end of the chiasma ridge. On the 

 right side it passes through the habenula and eminentia fimbriae; on the left side 

 through the caudal end of the primordium hippocampi. The cellular elements 

 of the eminentia thalami (em. th.) are well developed between the sulcus medius 

 and the sulcus intermedius. Between this region and the eminentia fimbriae is 

 an area containing fibers of the stria medullaris and poor in cells, which should 

 probably be associated with the lobus subhabenularis. 



Fig. 8 Section through the middle of the right habenula and the rostral part 

 of the thalamus. 



