Clinical Anatomy of the European Hamster 
empties into the caecum through a cone-shaped 
process forming the so-called "ileocaecal valve" 
{papilla ilealis). This valve marks the transition 
from caecum to colon. 
5.6.2.5 Structure of the Large 
Intestine 
The large intestine {intestinum crassum) extends 
from the ileocaecal junction to the anus. The tissue 
layers in the wall of the large intestine are similar 
in structure to those of the small intestine. The mu- 
cous membrane of the caecum and colon is pale, 
smooth and free of villi; it is thrown into numerous 
crescentic folds which correspond with the inter- 
vals between sacculi. The mucous membrane of the 
rectum is thicker, of a darker hue, more vascular 
and more loosely connected with the muscular coat. 
The epithelium of the caecum, colon and upper rectum consists of 
scattered mucous-secreting goblet cells and columnar absorptive cells 
with striated borders (Fig. 5-43). The solitary lymphatic follicles of 
the large intestine are most abundant in the submucous layer of the 
caecum. 
5.6.2.6 Caecum 
In European hamsters of good nutritional status, 
the caecum is a large structure (Figs. 5-36, 5-37, 
5-39) with a distinct apex (apex caeci) body {cor- 
pus caeci) and base {basis caeci). The caecum meas- 
ures up to 120 mm in length and 15 mm in width. 
The apex of the caecum lies in the left ventral part 
of the abdominal cavity and rests against the ab- 
dominal wall at an imaginary margin between the 
left lateral abdominal region {regio abdominis 
lateralis sinister) and the umbilical region. The cae- 
cum is bordered cranially by the visceral surface of 
the stomach, dorsolaterally by the descending colon 
and dorsomedially by the duodenum. The caecum 
proper, when distended, exhibits a helical shape 
(Fig. 5-36). The base of the caecum is freely mobile, 
consequently prohibiting exact establishment of its 
location. Neither taeniae nor haustra are recogniz- 
able in the caecum. The retaining capacity of the 
caecum exceeds that of the stomach. 
5.6.2.7 Colon 
The colon of Cricetus cricetus is divided into 
three parts: the ascending colon {colon ascendens), 
the transverse colon {colon transversum) and the 
descending colon {colon descendens) (Fig. 5-36). 
The ascending colon has a grayish-green serous 
surface and, depending on the age of the hamster, a 
length of about 350 mm. It commences with a 
broad S-shaped loop which lies dorsal to the apex 
of the caecum. In this area, the colon has a diameter 
of 10 to 12 mm, depending upon its distention; it 
gradually constricts as it runs dorsomedially (to 
the left) toward the apex of the caecum. It extends 
along the apex of the caecum to the cranial border 
of the epididymal fat tissue in males, while in fe- 
males it extends to the left inguinal region {regio 
ingmnalis sinister) at the level of the third or 
fourth lumbar vertebra, where it forms a horse- 
shoe-shaped loop (Fig. 5-44). Craniolateral to the 
urinary bladder, the ascending colon turns cranio- 
dorsally while continuing in an oblique direction 
to the level of the cranial pole of the right kidney, 
where it crosses the body of the caecum dorsally 
and the ileum and duodenum ventrally. At the 
cranial pole of the right kidney, it bends caudolat- 
erally; in the right lateral abdominal region, it 
forms a large S-shaped loop about 30 mm in diam- 
eter. From the right kidney, it extends to the ventral 
abdominal wall and, alongside the right abdominal 
wall, executes another bend of about 180°. From 
this flexure, the ascending colon doubles back by 
means of an arch open caudally and proceeds caudo- 
dorsally nearly to the level of the right kidney, 
turning 180° a second time. 
The distal part of the double loop is applied 
closely to the proximal part by means of a short, 
fatty, 5 mm long mesocolon which binds the two 
flexures together up to the level of the cranial pole 
of the right kidney. Between the kidney and the 
visceral surface of the right lateral lobe of the liver, 
the ascending colon becomes the transverse colon. 
Shortly before the U-shaped loop of the ascending 
colon, fecal formation begins (Fig. 5-44). 
The transverse colon has a length of 60 to 70 mm 
and its diameter is about 3 mm. The serous surface 
of the transverse colon is grayish-green in color. 
This segment of the colon runs caudal to the stom- 
ach and liver and ventral to the cranial segment of 
the duodenum, remaining perpendicular to the me- 
dian plane until it reaches the left abdominal wall. 
Here it turns caudally and at the end of the spleen 
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