1. The large intestine presents the typical primate course, with an ascending, transverse and descending colon. The ileo-cæcal junction is situated in the right iliac fossa.

2. The ascending and descending mesocola are still free, not having become adherent to the parietal peritoneum along the dorsal abdominal wall. Hence the caudal portions of the ventral surfaces of the two kidneys are still covered by the primitive parietal peritoneum.

3. The great omentum is not yet adherent to the transverse colon and mesocolon except for a short distance on the extreme right. At this point the dorsal layer of the omentum has begun to contract adhesions to the hepatic flexure of the colon and ascending colon, but the rest of the transverse colon is free. Differing from the human arrangement is a line of adhesion, uniformly present in these monkeys, between the dorsal surface of the omentum along its right edge and the ventral surface and right border of the cæcum and ascending colon, parts which normally are not adherent to the omentum in man.

4. Hence in tracing the omentum to the left of the limited adhesion to the hepatic flexure and ascending colon, i. e., nearly throughout the entire extent of the transverse colon, we find the membrane passing freely without adhesion over the cephalic surface of the transverse mesocolon, which preserves its original free condition, independent of the omentum. This arrangement is shown in the schematic sagittal section in Fig. 230.

5. Tracing the omentum dorsad beyond the transverse colon and mesocolon the pancreas is reached. Here we encounter the first extensive area of omental or mesogastric adhesion. The omental peritoneum continues over the ventral and caudal surfaces of the gland, investing the same, but the dorsal surface has lost its serous covering and is anchored to the ventral surface of the left kidney. Hence a sagittal section would show the arrangement of the monkey’s omentum as indicated in the schematic Figs. 229 and 230. Making now a general comparison of the peritoneal membrane of this animal with that of man, and of both with the preceding common embryonal condition, we can draw the following conclusions, indicated schematically in the five figures 228-232.

Figs. 228-232.—Schematic sagittal sections of dorsal mesogastriumand omental bursa, in man, monkey, and cat.

Fig. 228.—Common embryonal condition, as illustrated by cat, afterrotation and formation of omental bursa.

Fig. 229.—Area of adhesion between dorsal mesogastrium and primitiveparietal peritoneum in Macacus, producing condition shown in [Fig. 230].

Fig. 230.—Arrangement of great omentum as found in Macacusrhesus, shown without reference to areas of peritoneal obliteration.

Fig. 231.—Corresponding section of human adult peritoneumshowing, along dotted lines, area of peritoneal adhesion.

Fig. 232.—Section showing human adult peritoneum withoutreference 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).