60 



THE ANATOMY OF VEETEBKATED ANIMALS. 



(or myelencephalon) beMnd, and the cerebellum with the pons 

 varolii (which together constitute the 7)ietencephalon) in front. 



Fig. 19. 



Fig. 19. — Diagrammatic horizontal section of a Vertebrate brain. The 

 following letters serve for both this figure and Fig. 20 : — 3Ib, Mid- 

 brain. What lies in front of this is the fore-brain, and what lies 

 behind, the hind-brain. L. t. the lamina terminalis ; Olf, the ol- 

 factory lobes; Hmp, the hemispheres; Th.E, the thalamence- 

 phalon ; Pn, the pineal gland ; Py, the pituitary body ; FM, the 

 foramen of Munro ; CS, the corpus striatum ; Th, the optic tha- 

 lamus ; CQ, the corpora quadrigemina ; CC, the crura cerebri; 

 Cb, the cerebellum ; P V, the pons varolii ; MO, the medulla 

 oblongata ; /, olfactorii ; //, optici ; ///, point of exit from the 

 brain of the motores oculorum ; IV, of the pathetici ; VI, of the 

 abducentes ; V-XII, origins of the other cerebral nerves. 1, olfac- 

 tory ventricle; 2, lateral ventricle; 3, third ventricle; 4, fourth 

 ventricle ; -f-, iter a teitio ad quartum ventriculum. 



The floor of the middle cerebral vesicle thickens, and 

 becomes converted into two great bundles of longitudinal 



