[Illustration: FIG. 232.--Section showing human adult peritoneum without reference to area of adhesion.] 1. The dorsal layer of the monkey's omentum in its proximal segment behaves in the same way as in man, _i. e._, it becomes adherent to the primitive parietal peritoneum down as far as the caudal margin of the dorsal surface of the pancreas included between the primitive mesogastric layers forming by their further growth the omental apron. Therefore we find, as in the human subject, (_a_) The pancreas adherent to the ventral surface of the left kidney. (_b_) A portion of the ventral surface of the kidney, cephalad of the pancreas, and the dorsal wall of the retrogastric (lesser peritoneal) space lined by secondary parietal peritoneum derived from the third layer of the omentum (original right layer of dorsal mesogastrium). 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. 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.