No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 429 
Fig. 26. Two sections through the body are given in Figs. 
27 and 28. 
The amnion has become separated from the body with the 
exception of the part about the cord and also that along the 
right side of the body, over the heart. The arrow in Fig. 25 
shows how the amnion on that side is extended over the ventral 
body wall to make the 
condition shown in Fig. 
28. No doubt the cause _ PS 
of this is the rotation of ante he 
the body, throwing the ef Uy, 
cord to its right side and ides 
the amnion with it. In 
nearly all young embryos 
the cord is on the right 
side.1 With the excep- 
tion of the four instances 
mentioned below, the ro- 
tation has always been 
so as to throw the left 
side of the body away 
from the chorion, and in 
all of these specimens the 
amnion must have swept 
ever they body inom leit qe .6.— oven and Eiabryo No: XI enlareedeeaes! 
to right, as shown in the Just half of the ovum is shown. A,arm; /, leg; A, 
Dri, heart ; z v, umbilical vesicle ; B, branchial arch. 
figures. I find a similar 
illustration by His in his great monograph.? 
Absence of a Ventral Mesentery.— After the septum trans- 
versum has been formed as it is in embryo XII, there is on its 
ventral side a pretty sharp groove, which indicates that the 
umbilical vesicle is being constricted at this point. 
It is generally believed that the ventral mesentery of the 
intestine extends to the umbilicus, and that ultimately the round 
ligament of the liver represents its remnant after most of it has 
BS 
— 
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ae 

1 The exceptions have been published by Waldeyer: Studien des physiol. 
Inst. zu Breslau, 1865 ; Janogik: Arch. f. mik. Anat., Bd. 30; His: Anat. mensch. 
Embryonen, Plate VIII, Figs. A 1-4; Mall: Journ. of Morph., vol. V. 
2 His: Anat. mensch. Embryonen, Plate VI, Fig. 3, No. Io. 
