104 



NERVOUS SYSTEM 



M 



NK 



FIG. 141. PROFILE VIEWS OF THE BBAIN OF HUMAN EMBBYOS AT SUCCESSIVE STAGES, 

 BECONSTBUCTED FBOM SECTIONS. (His.) 



A. Brain of an embryo of about fifteen days (the embryo itself is shown in fig. 115) magnifiec 

 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; Z, diencephalon ; M, mid-brain; J, isthmi 

 between mid- and hind-brain ; Hh, cerebellum ; N, rhombic brain ; Gb, otic vesicle ; Bf, fourt 

 ventricle ; Nk, neck-curvature ; Br, pons-curvature ; Pm, mamillary process ; Tr, infundibuluro 

 Hp (in B), outline of hypophysis-fold of buccal ectoderm; 111, olfactory lobe. In C the basihxr arter 

 is represented along its whole course. 



