THE PERITONEUM 411 



It is areolar tissue, and is more or less loaded with fat according to the condition 

 of the subject, except over the diaphragm. It sends laminas into the various 

 peritoneal folds. 



The peritoneum, the serous membrane which lines the cavity, will be described 

 later. 



The abdominal walls are pierced in the adult by five apertures. These are 

 the three foramina of the diaphragm and the inguinal canals, which have been 

 described. In the fa;tus there is the umbilical opening also. This transmits the 

 urachus, a tube which connects the bladder with the allantois; the two umbilical 

 arteries, which carry blood from the foetus to the placenta; and the umbilical 

 vem, which returns blood from the placenta to the liver of the fcetus. After birth 

 the orifice is closed by fibrous tissue, leaving a scar, the umbilicus,' which is more 

 or less distinctly visible in the median ventral line in a transverse plane about 

 tangent to the ventral end of the last rib. 



The cavity contains the greater part of the digestive and urinary organs, part 

 of the internal genital organs, numerous nerves, blood vessels, lymph vessels and 

 glands, ductless glands (spleen and adrenal bodies), and certain fcetal remains. 



For topographic purposes the abdomen is divided into nine regions by imagi- 

 nary planes.i Two of these planes are sagittal and two are transverse. The 

 sagittal planes cut the middles of the inguinal ligaments; the transverse planes 

 pass through the last thoracic and fifth lumbar vertebra, or the ventral end of the 

 fifteenth rib and the tuber coxse respectively. The transverse planes divide the 

 abdomen into three zones, one behind the other, viz., epigastric, mesogastric, 

 and hypogastric : these are subdivided by the sagittal planes as indicated in the 

 subjoined table: 



Left parachondriao Xiphoid Right parachondriao 



Left lumbar Umbihcal Right lumbar 



Left iliac .Prepubic Right iliac 



Other useful regional terms are: sublumbar, diaphragmatic, inguinal. The 

 first two require no explanation. The inguinal regions (right and left) lie in front 

 of the inguinal ligament. The flank is that part of the lateral wall which is formed 

 only of soft structures. The triangular depression on its upper part is termed 

 the paralumbar fossa; this is bounded dorsally by the lateral Ijorder of the lon- 

 gissimus, ventrally by the upper border of the obliquus abdominis internus, and 

 in front by the last rib. 



THE PERITONEUM = 



The peritoneum is the thin serous membrane which lines the abdominal cavity 

 and the pelvic cavity (in part), and covers to a greater or less extent the viscera 

 contained therein. In the male it is a completely closed sac, but in the female 

 there are two small openings in it; these are the abdominal orifices of the uterine 

 or Fallopian tubes, which at their other ends communicate with the uterus, and so 

 indirectly with- the exterior. The peritoneal cavity (Cavum peritonei) is only a 

 .potential one, since its opposing walls are normally separated only by the thin 

 film of serous fluid (secreted by the membrane) which acts as a lubricant.^ 



The free surface of the membrane has a glistening appearance and is very 

 smooth. This is due to the fact that this surface is formed by a layer of flat mes- 



1 This method of division, although long in use, is practically valueless for accurate descrip- 

 tion. It is mentioned here chiefly because agreement on a more useful topographic method has 

 not been arrived at. 



^ Only a general account of the arrangement of the peritoneum is given in this section, since 

 a detailed description cannot be understood without a knowledge of the ^scera concerned. 



' It is necessary not to confuse the peritoneal cavity with the abdominal cavity. The 

 organs are all extraperitoneal and the peritoneal cavity contains only the serous fluid. 



