430 MALL. [Vou. XII. 
disappeared. This theory is expressed by two diagrams in 
Minot’s Embryology, page 767. As the liver begins to grow, 
and while the heart is being pushed down in front of it, the 
ventral end of the septum transversum is turned down to the 
umbilicus. While this is taking place the stem of the umbilical 
vesicle becomes relatively smaller and smaller, but there is no 
union between the umbilical vesicle and the septum transversum 
as expressed in Minot’s diagram. The first stage of this 

Fics. 27 and 28.— Section through Embryo XIX to show the Attachment of the Amnion to the 
Side of the Body. Enlarged 25 times. A, amnion; S, stomach; H, heart; c, cardinal 
vein; #, umbilical vein; a, aorta. 
process is shown in my Fig. 24, and its successive stages are 
shown in His’s A¢las, Plate IX. In all six embryos pictured 
on that plate the successive stages are represented, and in none 
of them is the umbilical vesicle attached to the septum trans- 
versum to form a ventral mesentery. From these embryos of 
His we can pass to embryo XIX, in which the umbilical vesicle 
communicates by a round canal with the intestine, and the 
tube is completely encircled with a space which extends to the 
liver, thus cutting off any possible ventral mesentery at that 
point. The same thing is shown, but in a later stage, in 
