II. RELATION OF GREAT OMENTUM TO TRANSVERSE COLON, TRANSVERSE MESOCOLON AND THIRD PART OF DUODENUM.
The second purpose to be accomplished by the study of the cat’s abdominal cavity at this stage is the correct appreciation of the adult human conditions which are produced by areas of adhesion between the transverse colon, transverse mesocolon and third part of the duodenum on the one hand, and the dorsal mesogastrium, as great omentum, with the structures contained between its layers, on the other.
Perform the manipulations of the large and small intestine in the cat (see p. 67) which are required in order that the tract may be arranged so that it will correspond in general to the topographical conditions presented by the adult human subject. Locate the transverse colon and mesocolon and the third portion of the duodenum produced by these manipulations in imitation of the corresponding human structures. Then proceed to plot the different parts out successively as they would appear in a sagittal section (Fig. 224).
[Illustration: FIG. 224.--Schematic sagittal section of abdominal viscera of cat, after the intestines have been rotated to correspond to the adult human disposition, to show lines of peritoneal reflection before adhesion.]
The following facts are to be noted and indicated on the plan of the section:
1. The great omentum is free, hanging down from the greater curvature of the stomach over the coils of intestine. Turning the omentum up it will be observed that the body of the pancreas is included between the two dorsal layers of the membrane.
2. The omentum, containing the pancreas, can be lifted up, exposing the next succeeding structure, viz., the transverse colon and mesocolon. In the cat the large intestine has been brought over, by the manipulations above indicated, into a transverse position so as to represent the human transverse colon and its mesocolon. It is therefore necessary to remember that in this mammal the fixation of the transverse mesocolon in the position indicated, by adhesion of ascending and descending mesocola to the parietal peritoneum of the abdominal background, has not yet occurred. Consequently the membrane must be held in the transverse position in order to represent the human arrangement.