84 PERCIVAL BAILEY 



1 wish here to express my indebtedness to Ur. C. J. Herrick, 

 whose broad knowledge and mature judgment has been of in- 

 vakiable assistance, and especially to Dr. Geo. W. Bartlemez, 

 at whose suggestion the work was undertaken and without whose 

 kindly interest the work would have been impossible. Thanks 

 are also due to Mr. A. B. Streedain for the care he has taken 

 with the illustrative work. 



MATERIAL AND METHODS 



The material upon which this study was chiefly based con- 

 sists of three very well preserved human embryos, cut in trans- 

 verse series, stained in bulk with, borax carmine, and counter- 

 stained on the slide with orange G. Wax-plate reconstructions 

 were made, the plates being stacked from a side view of the embryo 

 drawn from a photograph, taken after fixation. The shrinkage 

 after embedding was calculated and the outline reduced accord- 

 ingly. Although the primary object of this study is the mor- 

 phology and relations of the roof plate, in two cases the entire 

 forebrain has been modeled. This was done because the embryos 

 happened to fall in at opportune intervals between His' embryo 

 CR (13.6 mm.) and the embryo of 50 mm. also modeled by him, 

 and also in order that the relations of the choroid plexuses might 

 be seen more clearly. 



Embryo H 173 was obtained from an aborted ovum of 42 x 32 

 X 19 mm., presented by Dr. N. R. Engels of Chicago. The only 

 available history w^as that the patient had missed two menses. 

 The intact ovum was placed in physiological salt solution and 

 kept at about 0°C. for 11 hours. It was then opened and fixed 

 in formalin-Zenker for 24 hours, stained in bulk with borax 

 carmine, imbedded by the celloidin-paraffln method and cut 

 10m thick in a plane parallel to the hindbrain. The embryo 

 measi;red 19.1 mm., crown-rump length after fixation. The 

 sections were counterstained on the slides with orange G. The 

 total shrinkage was about 20 per cent. There are frequent 

 mitoses in embryo and chorion. The brain was modeled at a 

 magnification of 50 diameters with the aid of the Edinger pro- 



