1742 HUMAN ANATOMY. 



umbilicus (Fig. 1432). The umbilical vein runs in its free lower border to the por- 

 tal fissure of the liver, whence its continuation, the ductus venosus, passes to the 

 inferior vena cava. The anterior mesentery, containing the liver, is opposite to the 

 7nesogastriu?n, or mesentery of the stomach, which contains the spleen. The pan- 

 creas, although developed in both the anterior and the posterior mesenteries, lies 

 chiefly in the latter. As the jejuno-ileum enlarges it hangs in loops from the spine, 

 carrying folds of mesentery with it surrounding the vessels. The multiplication of 

 these folds gives rise to the complication of the adult arrangement. 



When two layers of a serous membrane come to lie permanently and practically 

 immovably upon each other, there is a tendency to fusion between them, the meso- 

 thelium covering the apposed surfaces disappearing and its place being taken by 

 connective tissue (Fig. 1472 j. Thus, when a mesentery lies against the abdominal 

 wall, the mesothelium of the parietal peritoneum and of the mesentery apposed to 

 it degenerates into connective tissue, and the peritoneum on the free surface of the 

 mesentery becomes a part of the permanent parietal peritoneum. Much of the 

 originally free parietal peritoneum is thus replaced by fusion with what once belonged 

 to a mesentery. 



The stomach undergoes rotation, so that the original left side becomes the 

 anterior and the posterior border the greater curvature. The mesogastrium grows 

 out of all proportion, so as not only to describe a curve to the left, but to hang 

 downward in a free fold. The loop of the duodenum turns to the right, so that all 

 of it, except the first part, lies against the posterior abdominal wall. The head of the 

 pancreas is carried with it. The serous covering of the back of the duodenum (in 

 its new position J, that of its mesentery, and that of the back of the head of the 

 pancreas disappear, fusing with the parietal peritoneum of the posterior abdominal 

 wall. 



The mesentery attached to the jejuno-ileum artd to most of the large intestine 

 becomes twisted as the gut returns into the abdomen from the umbilical cord, so 

 that the caecum is thrown upward and to the right to lie under the livier, whence it 

 descends to its permanent place ; hence the original right and left sides of the 

 mesentery change places. The mesentery of the ascending colon fuses with the 

 posterior covering of the right side of the abdomen ; that of the descending colon 

 to the sigmoid flexure does the same on the left. 



The sub- or retroperito7ieal tissue is very important. As above stated, there 

 is a thin fibro-elastic layer supporting the mesothelial cells, which is a part of the 

 serous membrane, although it is not present in the earlier stages. Beneath this 

 tunica propria there may be a continuous mass of connective tissue, to be compared 

 to dense, sponge-like cobwebs, which serves as a packing between different organs 

 and around vessels, nerves, and ducts. It may contain a large amount of fat. This 

 i^ particularly de\'eloped about retroperitoneal viscera and along the aorta. The 

 parietal peritoneum is usually thin where no fusion with another layer nor with 

 fasciae has occurred. 



We shall describe ( i ) the peritoneum of the anterior and lateral abdominal 

 walls, with its prolongations onto the diaphragm and into the pelvis ; (2) the folds 

 derived from the anterior mesentery ; (3) those from the posterior mesentery from 

 above downward. Most matters of detail are discussed with the various organs 

 having peritoneal relations. 



The Anterior Parietal Peritoneum. — Four folds diverge from the umbili- 

 cus, three running downward, symmetrically disposed, — namely, a median fold (plica 

 umbilicalis media), expanding to the top of the bladder covering the nrachus, a 

 fibrous cord representing the atrophied intra-embryonic segment of the allantoic 

 duct, and two lateral folds (plicae iinibilicales latcrales) containing fibrous cords, the 

 obliterated hypogastric arteries, continuous with the permanent superior vesical arte- 

 ries. If the bladder be distended, they can be traced to its upper lateral aspects ; 

 otherwise to the sides of the pelvis. The fibrous tissue of the obliterated arteries 

 becomes very scanty near the umbilicus. The supravesical fossa (fovea s-upravesi- 

 calis) or depression lies on each side above the pubes, between the median and 

 lateral folds. On the outer side of the latter, above the middle of Poupart's ligament, 

 is the interyial or mcdiaji ingui^ial fossa (fove^i inguinalis medialis), which is very 



