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FIG. 170. Diagrams of the brain in Vertebrates, showing the primitive regions and 

 their chief modifications. A, early stages, showing the anterior enlargement in three 

 lobes: I, II, and III, the primary vesicles. B, a sagittal section, showing the more 

 fundamental modifications of the walls of the primary brain vesicles. C, frontal section 

 of same. D, lateral view of the brain of the Frog. The vertical lines indicate 

 corresponding points in the different diagrams, i, 2, 3, and 4 are the ventricles of the 

 brain, c.c., crura cerebri; cer., cerebellum (hind brain); h, hemispheres (cerebrum or 



