Clinical Anatomy of the European Hamster 
5.3 ABDOMEN AND PERITONEUM 
Just as the thoracic cavity and its pleurae are not 
simply equivalent in the chest, so the abdominal 
and peritoneal cavities (cavum peritonei) are not 
coextensive. The peritoneal sac, but not the abdom- 
inal cavity, dips caudally into the pelvis. The ab- 
dominal space extends only to the pelvic inlet, while 
the peritoneum continues into the true pelvis, 
normally as far as the rectogenital and vesicogeni- 
tal pouches {excavationes rectogenitalis et vesico- 
genitalis). Accordingly, there are two sections, 
intra-abdominal and intra-pelvic, of one continu- 
ous peritoneal surface. 
Like the thoracic pleurae, the abdominal peri- 
toneum consists of a parietal part {peritoneum 
parietale), applied to the abdominal wall, and a 
visceral part (peritoneum uiscerale), reflected over 
the abdominal organs. Between the two surfaces is 
the peritoneal cavity, which — as with the pleural 
cavity — is only a potential space under normal con- 
ditions. It follows that no healthy tissue assembly 
is intraperitoneal. 
It follows also that some surface of each invagi- 
nating abdominal and pelvic organ is not covered 
by peritoneum, usually between attachments. Ac- 
cordingly, the extent of peritoneal reflection is a 
convenient criterion of intra-abdominal and intra- 
pelvic organization. Those organs almost com- 
pletely invested by peritoneum and only narrowly 
connected to the abdominal wall by peritoneum- 
covered connective tissue (carrying that organ's 
vascularization and innervation) are effectively 
suspended in the abdominal cavity by the parietal 
peritoneum. The suspensions represent the "liga- 
ments," omenta, mesenteries (of the small intestine) 
or mesocolons (of the large intestine) nearly sur- 
rounding the post-diaphragmatic digestive tube and 
its supportive glands (liver and pancreas) and the 
spleen. The non-suspended organs more closely 
applied to the abdominal wall, projecting negligi- 
bly into the cavity and covered by peritoneum only 
on their visceral surfaces, such as the kidney, rec- 
tum and bladder, or situated caudal to the pelvic 
inlet, are said to be retroperitoneal. 
Superficial to both visceral and parietal peri- 
tonea is a fibrous layer of connective tissue with 
more or less fatty tissue. Behind the parietal peri- 
toneum the layer merges with the fascia transversa- 
lis. It is often impossible to differentiate the sub- 
peritoneal fat from the underlying fascia, especially 
in the mesentery, mesocolon, renal and inguinal 
regions; fatty herniation is not uncommon. The 
transverse fascial planes blend with, and invest, 
the visceral surface of the abdominal musculature 
surrounding the cavity. The marked variations in 
abdominal contour reflect principally the state of 
distention of the viscera and the subcutaneous fat 
accumulation. In this elasticity, the abdomen differs 
from the thorax and other body cavities. 
The peritoneum is the abdominal expression of 
the pleural and pericardial layers. 
Each is histologically identical fluid-secreting serous membrane of 
mesothelial cells derived embryologically from one continuous body 
cavity, the coelom. 
The peritoneum is a lymph sac with great ab- 
sorptive power (solids via the lymphatics, liquids 
via the capillaries) and high secretory potential 
(abundant exudate with actively phagocytic mac- 
rophages on inflammation). 
The mesothelial pavement cells, each of which is cemented to its 
neighbors by an intercellular substance, can self-regenerate over small 
lesions. If the peritoneal tear is sufficiently large, repair is impossible, 
and the underlying connective tissue fibroblasts — which cannot form 
new serous cells — generate only fibrous adhesions. 
5.4 SEGMENTAL TOPOGRAPHY OF 
THE ABDOMEN 
The topography of the abdominal space can be 
divided into cranio- and caudomesocolic regions. 
A plane drawn transversely at the level of the first 
lumbar vertebra will intersect the stomach, 
pylorus and proximal duodenum, spleen, kidneys, 
pancreas, transverse colon and the root of the trans- 
verse mesocolon (Figs. 5-8, 5-9). The tissues lying 
between the transverse plane and the diaphragmatic 
arch are craniomesocolic; those lying between the 
plane and the pelvic inlet are caudomesocolic. This 
topography reflects a functional difference: the 
craniomesocolic, unlike the caudomesocolic, sys- 
tems are characterized bv tractable fixation, con- 
nection to the secretory ducts of liver and pancreas 
and deep cavity position. 
5.5 CRANIOMESOCOLIC REGION 
5.5.1 Craniomesocolic Peritoneum 
Viewed in a sagittal section and beginning at the 
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