ANATOMY OF A 17.8 MM, HUMAN EMBRYO 33 



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 INTRODUCTION 



This work was undertaken at the suggestion of Prof. C. S. 

 Minot, and carried on for the most part in his laboratory during 

 the years 1906 and 1907 when the author held an Austin Teach- 

 ing Fellowship in Histology and Embryology at the Harvard 

 Medical School. Its completion, unfortunately delayed by 

 other work, has been accomplished in the Anatomical Depart- 

 ment of the University and Bellevue Hospital Medical College. 

 During the progress of the work many helpful suggestions have 

 been received from Professors Minot and F. T. Lewis of Harvard, 

 and Prof. H. D. Senior of Bellevue, for which I am very grateful. 

 I also desire to express my gratitude to Mr. W. T. Oliver of 

 Lynn, Massachusetts, for the careful manner in which he has 

 reproduced in finished fonn my original drawings. 



The reconstructions upon which this work is based, were made 

 from transverse sections of Embryo 839 of the Harvard Embryo- 

 ^tT'i^cal Collection, chiefly by the modified graphic reconstruction 

 method of His. The shading usually has been inferred from a 

 study of the sections, but in a few instances wax models were 

 made of regions requiring a fuller interpretation. 



This embryo (extra-uterine) measured in formalin 17.8 mm., 

 greatest length, with a neck breech of 16.7 nmi. The greatest 

 length in 80 per cent alcohol was 13.6 mm. In previous papers 

 in which this embryo was referred to (Thyng '08, and Lewis and 

 Thyng '08), the latter measurement was given. 



EXTERNAL FEATURES 



The external features of this embryo are seen in profile view 

 in text figure 1, a reproduction of figure 104 in Minot's ('10) 

 "Laboratory text-book of embryology," also in part in plates 3 

 and 5. The neck-bend is approximately a right angle; the 

 cephalic flexure is also very nearly a right angled bend, so that 

 the oral aperture is in close proximity to the cardiac region. The 

 dorsal flexure has disappeared almost entirely, only a slight 

 elevation persisting to mark its earlier position. Above this 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 17, NO. 1 



