2. The monkey differs from adult man in the behavior of the dorsal omental layer in relation to the cephalic surface of the transverse mesocolon. The adhesion, which in the human subject fuses this layer with the transverse colon and mesocolon, does not occur in the monkey.

Figs. 233-235.—Series of schematic sagittal sections through left kidney and adrenal, pancreas, and transverse colon, to show development of adult peritoneal relations.
Fig. 233.—Embryonic condition, as illustrated by cat, after rotation of intestine. Pancreas free between dorsal layers of great omentum. Transverse colon and mesocolon free. Kidney behind primitive parietal peritoneum.
Fig. 234.—Area of adhesion between: 1. Primitive parietal peritoneum. 2. Mesogastrium forming great omentum. 3. Colon and mesocolon.
Fig. 235.—Adult human arrangement, shown without reference to obliterated areas.

Hence we have in this animal the following conditions:

(a) The omentum is non-adherent to the transverse colon and transverse mesocolon.

(b) The caudal surface of the pancreas is lined by its original mesogastric peritoneum.

(c) The transverse mesocolon is formed by the original two layers of the primitive dorsal mesentery; hence its cephalic layer is not “peritoneum of the lesser sac” as is the case in man.

(d) The caudal part of the ventral surface of the left kidney below the pancreas, is covered by the original parietal peritoneum.

(e) Only one point or line of secondary peritoneal transition exists, where the dorsal layer of the omentum in the adult becomes continuous with the parietal peritoneum covering the caudal surface of the pancreas and the ventral surface of the left kidney.

Note: In the schematic sections shown in [Figs. 228] to [232] the transverse colon is represented as far removed from the ventral surface of the left kidney, in order to make the peritoneal lines of the mesocolon more clear. Actually a sagittal section which would divide the kidney would cut the transverse colon at its extreme left end, where it turns close to the ventral surface of the left kidney and then follows its lateral border to form the splenic flexure ([Fig. 235]). The caudal part of the ventral surface of the left kidney in the adult human subject is covered by the peritoneum which, as secondary parietal peritoneum, is derived from the upper part of the right leaf (later ventral leaf) of the descending mesocolon. Hence it should be remembered that these diagrams present combinations of sections. A section which will show the full development of the transverse mesocolon is mesad of the kidney; while a section through the kidney would be too far laterad to show the transverse mesocolon.

Figs. 233, 234 and 235 show sagittal sections through the left kidney with the adult arrangement of the peritoneum and colon and the embryonic and adhesion stages leading to the same.