— 
out, is a diverticulum of the great sac which hes behind the stomach and adjacent 
organs, and which communicates with the great sac by a constricted passage, the 
foramen of Winslow. If the ereat sac be compared, as already suggested, to a bag, 
the anterior layer of which ¢ lothes the anterior and lateral walls of the abdomen 
and the posterior layer the viscera lying on the posterior wall, the small sac would 
correspond to a poc ‘ket lying be hind the upper part of the great sac, and opening 
into its cavity by a narrow jouth 1, on the right side, just below the liver. From 
this opening the pocket passes to the left be hind the lesser ome ntum, as far as the 
spleen, up behind the Spigehan lobe of the liver, and down behind the stomach, 
and into the great omentum. 
As in the case of the great sac, it will of course be understood that the two walls of 
the small sac and the boundaries of the foramen of Winslow are normally in contact. 
We shall first consider this opening, and then trace the layers of the small sac. 
Foramen of Winslow (lig. 709, AT iis, the constricted eee which leads 
from the great into the small sac of the peritoneum, is found just below and behind the 
portal fissure of the liver by running the finger along the under surface of the gall- 
bladder towards its neck, when, with little. difficulty, it passes behind the right 
margin of the lesser omentum and into the foramen, It is bounded in front by the 
free right border of the lesser omentuin, passing up from the first part of the duodenum 
to the portal fissure, and containing between its two layers the portal vein, hepatic 
artery, and bile duct. Behind, les the inferior vena cava, covered, of course, by 
peritoneum. Above, is placed the caudate lobe of the hver. And below, lie the first 
part of the duodenum, and the hepatic artery, the latter running forwards and to the 
right beneath the foramen, before turning up into the lesser omentum. It should 
be remembered that, normally, the various boundaries of the foramen lie in contact, 
and that its cavity can only be said to exist as such when its walls are drawn apart. 
If we follow the small sac,in through the foramen, it will be found that it 
expands immediately beyond this narrow opening (Fig. 707), its upper portion lying 
behind the lesser omentum, and running up behind the Spigelian lobe of the liver 
as far as its upper end; and its lower portion passing down behind the stomach 
and on into the great omentum, where it lies in front of the transverse colon, and 
extends practically to the lower end of the omentum—although this latter point 
cannot often be demonstrated in the adult. 
As the small sac is composed, like the great, of two distinct layers, an anterior 
and a posterior, 1t will be necessary to follow each of these separately. Above, the 
anterior layer of the small sac clothes the Spigelian lobe; 1t then passes down (from 
the posterior margin of the portal fissure, and the fissure of the ductus venosus) to 
the lesser curvature of the stomach as the posterior layer of the lesser omentum. 
Continued on from this, it clothes the inferior (or visceral) surface of the stomach 
as far as the great curvature, with the exception of the small “uncovered area’ 
below and to the left of the cardia (Fig. 674, B), but it does not actually come — 
in contact with the cesophagus itself, the back and right side of which are un- 
covered. On the left, it is reflected from the back of the stomach to the spleen as 
the deeper layer of the gastro-splenic omentum. 
From the great curvature of the stomach it is continued down, forming the 
posterior layer (of the anterior fold) of the great omentum; and at the lower part 
of the omentum it meets and becomes continuous with the posterior layer of the 
small sac. 
The posterior layer of the small sac, in passing through the foramen of Winslow, 
clothes the front of the vena cava (Fig. 709, A); beyond this, it covers the coeliac 
axis, and passes up to line the slight “depression on the posterior abdominal wall 
(diaphragm), against which the Spivelian lobe rests. Then, passing over to the left, 
it covers the upper surface of the pancreas, the top of the left kidney and suprarenal 
capsule, and the inner part of the gastric surface of the spleen (Fig. 710). From 
the anterior border of the pancreas it is prolonged forwards and downwards 
anterior or upper layer of the transverse mesocolon—to the transverse colon (Fig. 707). 
It next clothes the upper aspect of this gut, and is then continued down as the anterior 
layer of the posterior fold of the great omentum, almost to its lower border, where it 
becomes continuous with the anterior layer of the small sac, already described: 
1052 THE DIGESTIVE SYSTEM. 
