80 MARION HINES 
belonging to the Carnegie Institution, Laboratory of Embryology, 
Baltimore; the kindly interest of the late Dr. Franklin P. Mall 
and that of Dr. George L. Streeter. Also thanks are due Mr. 
A. B.-Streedain and Miss Marian Manly, of Chicago, for the 
drawings, to Miss Phelps, of Baltimore, for the microphotographs 
of the embryos belonging to the Carnegie Collection, and to Mr. 
Ralph Witherow, for drawings of models of those embryos. And 
I cannot neglect to acknowledge the debt I owe M. L. Fyffe for 
an interest, long sustained, in the outcome of this contribution. 
MATERIAL AND METHODS 
This contribution is based upon a study of human material 
belonging to the Embryological Collections of the Department 
of Anatomy, University of Chicago, and of the Carnegie Institu- 
tion, Laboratory of Embryology, Baltimore. For the elaboration 
of the technique used in handling human embryos, the Depart- 
ment at Chicago is indebted to Dr. G. W. Bartelmez. The 
details of this technique are given by Bailey (’16). There is 
no better human material than that belonging to the Carnegie 
Laboratory. Doctor Mall was able to secure the cooperation 
of clinicians so that the preservation of the embryos studied was 
the best our present technique can secure. Wax models of the 
brains studied at Chicago were made, while those belonging to 
the Carnegie were plaster casts poured by Mr. Heard. All 
these models have been checked many times with either the 
photographs or the outline projection of the brains in question, 
so that the writer believes them to be as accurate as our present 
methods allow. 
The embryos studied may be grouped as set forth in table 1. 
Besides these embryos the following were examined, although 
their various olfactory centers were not plotted. In all of them 
the same areas with the same histological differentiation were 
found (table 2). 
