i . | 
| SUBDIVISION OF THE ABDOMINAL CAVITY. 995 
diaphragm for the passage of the inferior vena cava, the cesophagus, and the aorta 
respectively ; the apertures in the pelvic floor, through which the rectum, the 
urethra, and the vagina in the female, reach the surface; the inguinal canal, 
through which the spermatic cord (or round ligament) passes, in leaving the 
abdominal cavity; and lastly, the erural canal, a small passage which runs ‘down 
from the abdomen along the inner side of the femoral vessels. The two latter con- 
stitute on each side two weak points in the abdominal wall, through which a piece 
of intestine occasionally makes its way, giving rise to inguinal or femoral hernia 
respectively. 
Extraperitoneal or Subperitoneal Connective Tissue (tela subserosa).—Betweenu 
the fascize which cover the deep surfaces of the abdominal muscles, and the peri- 
toneum which lines the cavity, there is found a considerable quantity of connective 
tissue, generally more or less loaded with fat, which is known as the extraperitoneal 
or subperitoneal connective tissue. This is part of an extensive fascial system 
which lines the whole of the body cavity, outside its various serous sacs, and is 
continued on the several vessels, nerves, and other structures which pass from these 
cavities into the hmbs and neck. 
In the abdomen it is divisible into a parietal and a visceral portion, both com- 
posed of loose connective tissue. The former lines the-cavity, whilst the latter 
passes forwards between the mesenteries and other peritoneal folds to the viscera. 
These two portions of the extraperitoneal tissue are perfectly continuous with one 
another, and contain in their whole extent a vascular plexus, through which a com- 
munication is established between the vessels of the abdominal wall, on the one 
hand, and those of the contained viscera on the other. 
The parietal oe ae is thin and comparatively free from fat over the roof and 
anterior wall of the abdomen, and here the peritoneum is more firmly attached 
than where the tissue is fatty and large in amount. In the pelvis, on the other 
hand, the tissue is loose and tatty, and, as such, it is continued up for some inches 
on the anterior abdominal wall above the pubes, to permit of the ascent of the 
bladder during its distension, and the attendant stripping of the peritoneum off this 
portion of the anterior abdominal wall. Here also the urachus and the obliterated 
hypogastric arteries will be found passing up in its substance. On the posterior 
wall the tissue is large in amount and fatty, particularly where it surrounds the 
ereat vessels and kidneys. 
From this latter portion especially, the visceral expansions are derived in the 
form of prolongations around the various branches of the aorta. These expansions 
are connected with the areolar coats of the blood-vessels and are conducted by 
them into the mesenteries and other folds of the peritoneum, and thus reach the 
viscera. 
The chief uses of this tissue are: (1) to unite the layers of the abdominal wall to- 
gether; (2) to connect the viscera to these walls and to one another in such a loose 
manner that their distension or relaxation may not be interfered with, which 
would not be the case if the connecting medium were firm or rigid; (3) in addition, 
it is a storehouse of fat, forms sheaths for the vessels and nerves, and establishes, 
through its vascular plexus, communication between the parietal vessels and those 
distributed to the abdominal viscera. 
SUBDIVISION OF THE ABDOMINAL CAVITY. 
The abdomen is divided naturally by the pelvic brim into two parts, the 
abdomen proper, and the cavity of the pelvis. The former of these is further sub- 
divided, artificially, into nine regions. 
The pelvic brim (Figs. 158 and 159, p. 214), which separates the two natural 
divisions of the cavity, is formed behind by the base of the sacrum, at the sides by 
the iliopectineal lines, and in front by the pubic crests. In the erect position it 
usually makes an angle of about 55 to 60 degrees with the horizontal. The two 
portions of the abdominal cavity which the brim separates meet at an angle, the 
abdomen proper running almost vertically upwards from it, whilst the pelvic 
cavity slopes backwards and downwards. 
= 
