No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 449 
account I have employed the term membrana reuniens where- 
ever possible to avoid confusion, and have usually employed 
the terms septum and primitive diaphragm as synonyms. 
There are developed within the region of the septum trans- 
versum the whole liver, including its ventral mesentery, the lesser 
peritoneal cavity, the stomach, and the suprarenal capsule. 
This same region which I have marked out by these three 
boundaries as the septum transversum is still sharply defined 
in the adult. The point O in Figs. 16 and 30 is still as defin- 
ably marked as ever by the round ligament, foramen of Wins- 
low, and the duct passing from the liver to the duodenum. 
The round ligament is developed by the umbilical vein shift- 
ing around the side of the abdominal walls into the ventral 
mesentery of the liver, and then when the liver is retracted 
from the umbilical cord, the vein and mesentery remain as the 
round and broad ligaments respectively. 
Lesser Peritoneal Cavity.—I have already discussed the 
lesser peritoneal cavity in a separate paper,! and find that I can 
confirm all that I have stated at that time. I can only add 
that the portion of it extending up under the lung degenerates, 
while the omental sac is growing rapidly. I have also found 
that it is extremely easy for the omentum to find its way over 
the large intestine. At the time this takes place the large in- 
testine is in the median line, while the stomach and the omen- 
tum are on the left side of the body. After the intestine is 
retracted from the cord the caecum falls over to the right side 
of the body, while the descending colon is shifted to the left 
side, and the omentum then comes to lie on the ventral side of 
the transverse colon. 
Expansion of the Body Cavity and Obliteration of the Extra- 
embryonic Coelom.— After the pleural and pericardial cavities 
are separated from each other it is very easy to follow their further 
development. In embryo II, Fig. 47, the heart is still upright, 
and a transverse section of it is also transverse to the lung. 
The pleural cavity lies wholly on the dorsal side of the pericar- 
dial, Fig. 32. In the next stage, as the lungs descend more and 
more, the heart is tilted over so that its base is towards the 
1 Mall: Journ. of Morph., vol. V. 
