THE PERITONEUM. 987 



Below the umbilicus we have already noted the five longitudinal folds and the 

 inguinal fossae (p. 963). 



The parietal layer passes from the anterior wall to the under surface of the 

 diaphragm and clothes it up to the central tendon where the oesophagus and vena 

 cava inferior pass through. From here it spreads out on one side to the liver, on 

 the other to the stomach and spleen, and so changes into the visceral layer. 



The parietal peritoneum of the posterior abdominal wall rests on small and 

 limited spaces and passes over such structures as the kidneys, transverse duo- 

 denum, right and left colons, great vessel trunks, many lymph-glands and vessels 

 and nerve-plexuses. 



By means of a loose fatty connective tissue called retroperitoneal cellular tissue 

 these structures fasten themselves together and themselves to the peritoneum. 

 On this posterior wall to the left of the duodenum there may be as many as three 

 infoldings or retroperitoneal pouches which will be described later. 



Upper Wall of the Peritoneal Sac. 



The lower surface of the diaphragm representing the roof of the abdomen is 

 not covered wholly by peritoneum. Behind the central tendon it is partly free 

 where the surface of the liver rests upon it and where the suprarenal capsules and 

 kidneys come in contact with it. The greater part of the diaphragmatic covering 

 is directly continuous Avith the anterior and lateral parietal layers, and is distin- 

 guished by its extreme delicacy and firm connection, with the endo-abdominal 

 fascia. In the cleft-like holes left between the costal and sternal parts of the 

 diaphragm and between the costal and vertebral parts, peritoneum and pleura 

 meet; these are called "weak places," and here a diaphragmatic hernia can be 

 acquired. 



A small surface of the diaphragm situated behind the lobus Spigelii gets a 

 covering from the upper end of the posterior wall of the lesser sac which does not 

 enter into continuity with the serous covering of either side, but on the left it turns 

 into the mesial layer of the gastro-splenic omentum and on the right into the 

 mesial layer of the hepatico-renal ligament. 



Inferior Wall of the Peritoneal Sac. 



This belongs in part to the false pelvis and in part to the true pelvis. In the 

 former it is connected with the fascia iliaca. In the iliac fossa the peritoneum ex- 

 tends itself underneath and behind the caecum so that that structure hangs free in 

 the peritoneal cavity. There is usually no mesocaecum in the adult. Near the 

 caecum there are periccecal fossce, for later description. On the left side the peri- 

 toneum passes from within and Avithout over the iliacus muscle and fascia to the 

 formation of a very movable fold Avhich surrounds the siginoid flexure, the meso- 

 ngmoidea or sigmoid mesocolon. Where this attaches to the intestine, opposite 

 the brim of the true pelvis, the peritoneum raises itself into a fold Avhich has been 

 called lig. mesenterico-mesoeolicum (W. Gruber), which on one side runs into the 

 mesentery proper and on the other into the mesocolon of this flexure. It seems 



to have the purpose of limiting the deep descent of the rectal limb of the sicrmoid 





 flexure. 



In the left leaf of the mesosigmoidea is usually to be found the fossa subsig- 

 moidea or intersigmoidea. 



In the hollow of the true pelvis the peritoneum clothes that region of the lateral 

 wall Avhich in man extends between rectum and bladder, in Avoman betAveen rec- 

 tum and vagina, also between rectum and uterus. In the first it forms a pouch 

 open abo\ r e, excavatio recto-vesicaUs or recto-vesical pouch. The mouth of the 

 pouch is bounded by a crescentic fold of peritoneum on each side, the plica semi- 

 lunaris. The left one is usually the larger. They form the posterior false liga- 

 ments of the bladder. The depth of this pouch extends to Avithin one inch of the 

 prostate or Avithin about 8 cm. of the anal orifice. 



