THORAX AND ABDOMEN OF THE HORSE 101 



The last point to notice is the fixation of the dorsal sac of the 

 caecum and the terminal part of the right dorsal colon to organs on the 

 dorsal wall of the abdomen (right kidney and pancreas) and to a small 

 area of the wall itself. Fixation is eflfected by fibrous tissue (in which 

 are blood vessels and nerves), surrounded by a reflection of peritoneum, 

 and an offshoot from the right triangular ligament of the liver. 



The right and left portions of the ventral colon carry four taeniae 

 and four rows of sacculations. These two parts of the intestine, it will 

 be noted, are approximately equal in width. The pelvic flexure and 

 the greater part of the left dorsal colon are much narrower than the 

 rest and carry only one longitudinal band. The rest of the colon, 

 gradually dilating until it ends as the widest part of the tube, has 

 three taeniae. 



The small colon consists of coils mixed with those of the small 

 intestine in the left dorsal fourth of the abdominal cavity. Because of 

 the presence of a definite and broad mesentery, this part of the large 

 intestine is capable of a considerable degree of mobility. Like the 

 great colon, the small colon is characterised by sacculations and 

 taeniae. The bands are two in number: one following that border of the 

 intestine to which the mesentery is attached, the other running along 

 the convex border of the gut. 



The examination of the terminal part of the large intestine, the 

 rectum, must be postponed until the contents of the pelvis are 

 dissected. 



Peritoneum (Peritonaeum). — The peritoneum ^ is an elastic, smooth, 

 moist and glistening serous membrane that covers, more or less 

 completely, the surface of the organs contained in the abdomen, and also 

 lines the inner surface of the abdominal walls. It is continued beyond the 

 limits of the abdomen proper, clothes part of the pelvic organs, and lines 

 part of the pelvic wall. The part within the pelvis will be examined later. 

 A layer of areolar tissue, containing a variable amount of fat, connects 

 the peritoneum to the walls and viscera. In some places the tissue is 

 abundant, while in others, especially over the viscera, it is scanty in 

 amount. The presence of subserous tissue gives a fiocculent appearance 

 to the detached membrane. 



Like other serous membranes, the peritoneum is described as 

 consisting of two layers : a parietal layer (lamina parietalis) adherent to 

 the abdominal wall, and a visceral layer (lamina visceralis) applied to 

 the abdominal organs. Between the two is a potential space, the 

 peritoneal cavity, which is opened into when the wall of the abdomen is 



1 irepLTovaiov (peritoiiaion) [Qr.] = 7rept (peri), around + retrnt- (teiiiein), to stretcli. 



