Fig. 70. PROFILE VIEWS OP THE BRAIN OF HUMAN EMBRYOS AT THREE SEVERAL STAGES, 



RECONSTRUCTED FROM SECTIONS (His). 



A. Brain of an embryo of about 15 days (the embryo itself is shown in fig. 117) 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 ; H, vesicle of cerebral hemisphere, first secondary vesicle ; Z, thalamencephalon, 

 second secondary vesicle; M, mid-brain; /, isthmus between mid- and hind-brain; Hh, fourth 

 secondary vesicle ; N, fifth secondary vesicle ; Gb, otic vesicle ; Rf, fourth ventricle ; Nk, neck 

 curvature ; Br, pons curvature ; Pm, mammilary process ; Tr, infundibulum ; Up (in B), outline of 

 hypophysis-fold of buccal epiblast ; Rl t olfactory lobe. In C the basilar artery is represented along its 

 whole course. 



