THE EMBRYO. 



1175 



NK. 



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

 Cms.) (Copied from Quain's Anatomy.) 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. 

 31. Mid-brain. /.Isthmus between mid- and hind-brain. Hh. Fourth secondary vesicle. N. Fifth secondary 

 vesicle. Ob. Otic vesicle. Rf. Fourth ventricle. A T A'. Neck curvature. Br. Pons curvature. Pm. Mammillary 

 process. Tr. Infundibulum. Hp. (in B). Outline of hypophysis-fold of buccal epiblast. Jil. Olfactory fold. In 

 c the basilar artery is represented along its whole course. 



