THE PERITONEUM 411 
Tt is areolar tissue, and is more or less loaded with fat according to the condition 
of the subject, except over the diaphragm. It sends lamine 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 foetus 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 
vein, which returns blood from the placenta to the liver of the foetus. 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 foetal remains. 
For topographic purposes the abdomen is divided into nine regions by imagi- 
nary planes.!. Two of these planes are sagittal and two are transverse. The 
sagittal planes cut the middles of the mguinal ligaments; the transverse planes 
pass through the last thoracic and fifth lumbar vertebre, or the ventral end of the 
fifteenth rib and the tuber cox 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 parachondriac.......... UAVS ClPeobovcacooedes Right parachondriac 
ertnlmbars yer ace cies * Wanaorli cal es eaters stare Right lumbar 
MGC R HINTS Craven etctetansis sats. erste Prepubicwercrsccnya cece steve 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 border 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 peritonzi) 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- 
_ 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 viscera concerned. 
‘Tt 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. 
