THE EMBRYO. 



1175 



z. 



Eh. 



Pf. 



NE. 



FIG. 723. Profile views of the brain of human embryos at three several stages, reconstructed from sections. 

 iHis. i (Copied from Quain's Anatimui.\ A. Brain of an embryo of about fifteen days, magnified 35 

 diameters. B. Brain of an embryo about three and a half weeks old. The optic vesicle has been cut away, 

 c. Brain of an embryo about seven and a half weeks old. The optic stalk is cut through. A. Optic vesicle. 

 //. Vesicle of cerebral hemisphere, first secondary vesicle. Z. Thalamencephalon, second secondary vesicle. 

 .V. Mid-brain. ,7. Isthmus between mid- and hind-brain. Hh. Fourth secondary vesicle. X. Fifth secondary 

 vehicle. Gb. Otic vesicle. Rf. Fourth ventricle. .VA'. Neck curvature. Br. Pons curvature. Pm. Mammillary 

 process. Tr. Infundibulum.' lip. (in B). Outline of hypophysis-fold of buccal epiblast. Rl. Olfactory fold. In 

 c the basilar artery is represented along its whole course. 



