468 Description of a 4-mm. Human Embryo 
arate openings (a and y). Here again this embryo differs from those 
previously described or modelled, in all of which a single channel leads 
from sinus venosus to right auricle. Dr. Minot has recorded separate 
openings into the heart for the cardinal and omphalo-mesaraic veins in 
the chick (Textbook, p. 282), but the double openings just described do 
not appear to be correlated with those in the bird. 
4 ; ‘a re Lar Ai % 
Fig. 10. Model of heart, posterior view. X 90. 
The heart lies in the body cavity or ccelum, and is attached to the body 
wall by the sinus venosus, and to the intestinal tract by a short fold of 
mesenchyma. Fig. 10 shows also a portion of this intestinal tract; the 
mesodermal part has been partially dissected away from the entoderm 
in order to show the outgrowth destined to become the lung (Lu.). This 
outgrowth, situated at the level of the left auricle on the ventral side of 
