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DEVELOPMENT OF INTESTINAL CANAL AND PERITONEUM. 1057 
behind the stomach and lesser omentum. This portion of the cavity becomes the upper 
part (vestibule) of the small sac, and at first it communicates with the general cavity by 
a wide opening to the right 
bs = Stomach 
of the lesser omentum ; but | 
Mesentery obliterated 
the growth of the liver, en- ees Middle li 
Mt oe | bey tl : Re ate \| Crecum | Middle line 
croaching upon the opening, Dados Wee niicanSvoneennesonclen 
and other causes, reduce it 
to a relatively small size, 
and it forms the foramen 
of Winslow in the adult. 
The great omentum is, 
as pointed out above,.a bag- 
like growth of the lower 
part of the mesogastrium, 
which passes downwards 
and to the left in front of The 
the transverse colon. As mesentery 
shown in Fig. 713, A and B, 
it is at first entirely uncon- Rectum 
nected with the transverse Mesentery of descending colon 
colon and mesocolon; but — FyG. 712.—Two DIAGRAMS TO ILLUSTRATE THE DEVELOPMENT OF THE 
Descending 
-mesocolon 
obliterated 
Cecum 
Pelvic 
(sigmoid) 
mesocolon 
The mesentery 
about the third or fourth MESENTERIES. 
month it becomes united {[p the first figure the rotation of the intestinal loop and the continuous 
to both, and the adult con- primitive mesentery is shown. In the second figure (to the right), 
which shows a more advanced stage, the portions of the primitive 
Aare mesentery (going to the ascending and descending colons) which dis- 
on ). appear, through their adhesion to the posterior abdominal wall, are 
It would appear that the shaded dark ; the portions which persist are lightly shaded. 
growth of the lower part of i 
the small sac, and of the great omentum, is primarily due to a proliferation of the cells over a 
limited area of the mesogastrium, and a resulting folding of this layer downwards and to the left. 
dition is established (Fig. 
In the upper part of the mesogastrium the spleen is developed, and the portion of 
this fold which intervenes between the stomach and spleen forms the gastro-splenic 
omentum, whilst the part be- 
hind the spleen becomes the 
lieno-renal ligament. 
Of the primitive mesentery, 
the portion connected with the 
stomach — the mesogastrium 
-—becomes modified in the 
manner just described. The 
next division—the meso- 
duodenum — disappears com- 
pletely, owing to the turning 
over of the duodenal loop on 
to its right side, and its 
subsequent adhesion to the 
posterior abdominal wall, 
accompanied by the absorp- 
tion of its mesentery. The 
mesenteries of the small and 
A, shows the beginning of the great omentum and its independence of laree intestine are continuous 
the transverse mesocolon ; in B, the two come in contact ; and in 2 a 5 
C, they have fused along the line of contact. (According to Lock- at first (Fig. 7 Il). W hen the 
wood, the two layers of the fold shown in A, running in between Yrotation of the intestinal loop 
the great omentum and transverse mesocolon, instead of fusing, as takes place around the superior 
shown in B, are drawn out—unfolded—producing the condition mesenteric artery (see above), 
shownin ©). A, stomach ; B, transverse colon ; C, small intestine ; y 
D, duodenum ; E, pancreas ; F, great omentum ; G, placed in great the beginning ot the large 
sac ; H, in small sac of peritoneum. intestine, with its mesentery, 
is carried to the right across 
the duodenum, and a fan-shaped portion of the general mesentery, lying within the 
concavity of the loop, is partially cut off; this, later on, forms the mesentery proper in 
the adult. At first it is continuous by its rigbt border with the mesentery of the 
ascending colon, a part of the primitive mesentery (which is similarly continued into the 
mesentery of the transverse, descending, iliac, and pelvic colons). Subsequently, as 
67 
Fic. 713.—DIAGRAMS TO ILLUSTRATE THE DEVELOPMENT OF THE 
GREAT OMENTUM (after Hertwig). 
