A THEEE WEEKS' HUMAN EMBRYO, WITH ESPECIAL 



REFERENCE TO THE BRAIN AND THE NEPHRIC 



SYSTEM. 



SUSANNA PHELPS GAGE, 

 Embryologic Laboratory, Cornell University. 



With 5 Plates. 



The specimen under consideration was loaned to me sometime ago by 

 Dr. Mall for the investigation of the evidence of segmentation in the 

 brain of the higher mammals. 



While the study of this embryo is of necessity incomplete in the present 

 state of knowledge, certain points were shown so clearly by it, that they 

 are here presented. 



These points are: — For the central nervous system (a) the approxi- 

 mate location of the morphologic front of the brain, and (b) the location 

 of folds and lobules of the fore- and hind-brain which may have segmental 

 significance; for the nephric system, (a) the presence of a pronephros 

 and (b) a generalized state of the mesonephros, illustrating well-known 

 conditions in the lower as well as in the higher forms. 



Other facts which agree with or differ slightly from those generally 

 accepted are presented incidentally. 



The specimen is No. 148 of the Johns Hopkins University Medical 

 School Collection gathered by Dr. Mall, sectioned under his direction, 

 and most generously opened for inspection to students. In the catalogue 

 of this collection ' is found a list of nine papers which use this specimen 

 to illustrate special points. These will be referred to under the proper 

 headings. 



The embryologic collections of Cornell University and of the HarvarG 

 and Johns Hopkins Medical Schools were also freely placed at my com- 

 mand for study and comparison. 



' Mall, F. P., Johns Hopkins Hosp. Bull., XIV, 1903. Catalogue of the 

 collection of human embryos in the Anatomical Laboratory of the Johns 

 Hopkins University. Baltimore, 1904. 



Amehica.n Jouknal of Anato.my. — Vol. IV. 



