102 



200LOGY. 



vesicle is the fourth ventricle ; while that of the second 

 vesicle, being reduced to a narrow passage, received 

 from early anatomists the pompous title of Her a tertio 



Fig. 56. BRAIN OF RABBIT. 

 Diagram of a horizontal section. 



Fig. 57. BRAIN OF RABBIT. 

 Diagram of a median (sagittal) section. 



ad quartum ventriculum : modern biologists abbreviate 

 this to the simple word iter, The difference in the num- 

 bering of the embryonic vesicles and the adult ventricles 



