348 



ol. 



PIG. 172. Diagrams of the brain in Vertebrates, bowing the primitive regions a d their chief 

 modifications. A, early stages, showing the anterior enlargement in three lobes: I, II, andJIIt the 

 primary vesicles. B, a sagittal section, showing the more fundamental modifications of the walls 

 of the primary 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 ven- 

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

 fore brain); inf., infundibulum; med., medulla oblongata; mes., mesencephalon or mid brain; met., 

 metencephalon or hind brain; my., myencephalon or medulla; n 1 , olfactory nerve; n*, optic nerve; 

 ol., olfactory lobe; op., optic lobes; o.th., optic thalamus; pr., prosencephalon, or fore brain; .., 

 pons Varolii; s.c., spinal cord; th., thalamencephalon or "between" brain. 



