HEAD AND NECK OF THE HORSE 179 



diencephalon. From the former the hollow cerebral hemispheres rapidly grow, and, 

 becanse of their extension in a backward direction, soon override the diencephalon 

 and, later, the mesencephalon. The cavities of the hemispheres become the lateral 

 ventricles, connected with the rest of the cavity of the fore-brain by a wide opening 

 that gradually narrows to the dimensions of the interventricular foramen of the 

 adult brain. 



The lateral walls of the diencejihalon form the thalami, while the ventral wall 

 thickens into part of the cerebral peduncles and the structures that occupy the 

 interpeduncular fossa. It is noteworthy that the roof plate of the diencephalon, like 

 that of the myelencephalon, remains thin and membranous. 



The following table indicates generally the parts of the adult brain that develop 

 from the primary embryonic vesicles : — 



o 



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O 



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OS-" tj .^ f. n-t 



3 5? -• -S =■ ^ £ 



^^ -SgS -SI'S E^-S I -I E^sj S-S.^ii -g^^sgs 



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-5 2 -3- cd 



'^ — CO _c 



^ 2 S S^ S^ 



2 S 



5 -S ^ "S 



o 

 o 



