998 THE DIGESTIVE SYSTEM. 
its complete description until the various organs, with their special peritoneal 
relations, have been separately considered. Nevertheless, it will be necessary to 
give here a general account of the disposition of the membrane, and to refer to 
the three varieties of folds which it forms in passing from organ to organ, or from 
these to the abdominal wall. 
The peritoneum (tunica serosa) 1s the serous sac which lines the abdominal 
cavity and invests most of the abdominal viscera, to a greater or less degree. Like 
the pleure, the tunica vaginalis of the testicle, and other serous sacs, its walls are 
composed of a thin layer of fibrous tissue, containing numerous elastic fibres, and 
covered over on the side turned towards the cavity of the sac by flattened 
endothelial cells. Like them, too, the peritoneum in the male is a completely 
closed bag, but in the female this is not the ease, for the abdominal end of each 
Fallopian tube opens into the sac, whilst the other end of that tube communicates 
with the uterus, and thus, indirectly, with the exterior. Normally the membrane 
secretes only sufficient moisture to lubricate its surface, otherwise the sac is 
perfectly empty, and its opposing walls lie in contact, thus practically obliterating 
its cavity. 
The use of these lubricated and highly polished serous lnings, found in the 
abdomen and certain other cavities, is to fac ilitate, and render, as far as possible, 
frictionless, the movements of the contained viscera during any changes in size or 
form which they or their con- 
taining cavity may undergo. As 
a result of this arrangement, not- 
Liver withstanding the tonic pressure 
of the abdominal wall on its 
Lesser_ [| — Small sac contents, the stomach and in- 
aaa Ween ren testines are free to move with 
arrow passed the greatest ease and the least 
F friction, when any change takes 
OME place either in the organs them- 
Jf Third partof selves or in their surroundings. 
uaa The peritoneum is a thin 
ioe" olistening membrane, which may 
Stomach— 
‘Transverse 
mesocolon 
Great 
omentum 
varnish applied to the inner aspect 
of the abdominal walls, and to the 
surface of the contained viscera, 
except where these are directly ap- 
pled to the walls or to one another. 
ore It forms throughout its entire 
\ ans ie extent a continuous and distinet 
~ Douglas sheet, but 1t is united so inti- 
mately to the viscera, and follows 
the irregularities of their walls so 
closely, that it appears at first 
sight to be a superficial layer of 
these walls, rather than a separate 
membrane. Outside the peri- 
a ee ec vated ea Rent toneum lies the subperitoneal con- 
My ‘the peritoneum is black and is represented ae beme DeCtives tissue—already deseribed 
much larger than in nature ; the small sac is very darkly —which connects it more or less 
shaded ; the peritoneum on section is shown as a white intimately to the fascial hning ot 
line; and a white arrow is passed through the foramen of the abdominal walls, and to the 
Winslow from the great, into the small sae. p : 
abdominal viscera. 
If we trace the peritoneum as a continuous layer, .eginning in front we find 
that it lines the deep surface of the anterior abdominal wall, and is continued 
upwards to the under surface of the diaphragm (Fig. 672), the greater portion 
of which it covers. From the posterior part of the diaphragm it is reflected or 
carried forwards on to the upper surface of the liver, and then down over the 
—The mesentery 
Small ANTS \ 
intestine \ 
Uterus— 
Bladder a 
a 
aptly be compared to a coat of 
al 
