A HUMAN EMBRYO OF THIRTEEN SOMITES 



IVAN E. WALLIN 



Anatomical Laboratory, Bellevue Hospital Medical College, New York City 



SEVEN FIGURES 



The embryo which forms the basis of this work was given to 

 me by Dr. Rudolph Boencke in the spring of 1911.' It has been 

 placed in the collection of the Department of Anatomy at the 

 University and Bellevue Hospital Medical College and is called 

 embryo no. 4. 



The embryo was aborted two weeks after the last menstrual 

 period. There was no record of coitus. After fixation and with 

 the amnion intact the embryo measured 2.3 mm. in length. It 

 was cut into transverse sections 5 m in thickness, and stained 

 with iron haematoxylin. The embryo yielded 287 sections. 



Wax plate reconstructions were made of the complete embryo, 

 the heart, the foregut, also of the caudal part of the medullary 

 tube with the hind-gut and the belly stalk vessels. A graphic 

 reconstruction was made representing the embryo cut in the 

 mid-sagittal plane. All the reconstructions were made at a mag- 

 nification of 200. 



The embryo appears to be normal in every respect and the 

 following points of structure have been determined. 



EXTERNAL FORM 



In its general configuration this embryo is very similar to 

 Pfannenstiel III described by Low ('08). The body has a regu- 

 lar dorso-ventral curve and has a slight twist so that the head is 

 situated to the right of the mid-sagittal plane. The yolk sac 

 communicates with the primitive gut by means of an extensive 

 yolk stalk. The latter has its greatest diameter in the cephalo- 



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