DISSECTION OF THE DOG 23 



It IS best to commence the examination of the peritoneum where its 

 disposition is simplest. This will be found to be the case in the more caudal 

 part of the abdomen. If, then, the arrangement of the peritoneum be followed 

 in a transverse direction a short distance from the entrance to the pelvis it 

 Mill be found that the ventral, lateral, and dorsal walls of the abdomen are 

 clothed by parietal peritoneum. This is reflected from the dorsal wall along 

 a Ime a little to the left of the, median plane, in order that the descending colon 

 may be encircled. The membranous double layer ^vhich connects the descending 

 colon to the abdominal parietes is named the descending mesocolon (mesocolon 

 descendens), and is continued as a similar dupUcature associated with the 

 transverse colon, the transverse mesocolon (mesocolon transversum) , and beyond 

 this again on to the terminal part of the ascending colon as the ascending 

 mesocolon (mesocolon ascendens). 



The peritoneum should now be followed in a transverse direction at a level 

 nearer the diaphragm ; opposite, let us say, the commencement of the ascending 

 colon. Beginning on the left side of the abdomen, the parietal peritoneum 

 lines the lateral and dorsal walls of the cavity as far as the margin of the kidney, 

 where it is continuous with the base of the descending mesocolon. Here it 

 is diverted in a ventral direction in order to enclose the spleen. The membrane 

 from the base of the mesocolon to the spleen is a part of the greater omentum. 

 From the right face of the descending mesocolon a double layer of peritoneum 

 extends over to the right side of the abdomen and encloses the various parts 

 of the duodenum, the pancreas, and the commencement of the ascending 

 colon. The jejunum and ileum are suspended from the dorsal wall of the 

 abdomen by the mesentery (mesenterium), a double fold of peritoneum, fan- 

 shaped in form. 



The peritoneum should now be followed in a longitudinal direction beginning 

 with the very obvious greater omentum (omentum majus). On first opening 

 the abdomen, the greater omentum is revealed covering the whole of the 

 intestinal mass, and extending from the stomach and spleen, on the one hand, 

 to the pelvic entrance on the other. A careful examination of the omentum 

 discloses the fact that it is formed by two membranes ; or, rather, by one 

 membrane folded on itself, so that the folded margin lies in the region of the 

 pelvis and the right side of the abdomen. Still closer examination shows that 

 there are really four layers of peritoneum in its constitution. Two ventral 

 layers are closely applied to each other, and two dorsal layers are similarly 

 intimately related. Between the united layers there may be a considerable 

 accumulation of fat. 



If the two ventral layers of the omentum are followed to the stomach they 

 will be found to separate at the greater curvature of this organ so as to form 

 serous coverings for its two surfaces. At the lesser curvature they again 

 come together and form a thin membrane, the lesser omentum (omentum minus), 

 which extends from the lesser curvature of the stomach to the margins of the 



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