The Anatomy of the Human Peritoneum and Abdominal Cavity / Considered from the Standpoint of Development and Comparative Anatomy

by George S. Huntington

It will be observed that in all the schematic sections of the early embryonic stages the two layers of the transverse mesocolon are shown without dorsal attachment, as turning with the formation of a fold ([Fig. 228] at x) into two layers descending ventrad of the parietal peritoneum. This is because the dorsal attachment of the mesocolon is at this stage still in the median line and would hence not be encountered by a sagittal section through the kidney, and because the two layers of the transverse mesocolon, immediately after rotation of the large intestine, are still directly continuous with the two layers of the descending mesocolon. That is to say, the cephalic layer of the transverse mesocolon is continuous with the dorsal (originally the left) layer of the descending mesocolon, and the caudal layer of the transverse mesocolon with the ventral (originally the right) layer of the descending mesocolon, which is, in the human subject, to assume subsequently the character of parietal peritoneum after the dorsal layer and the primitive parietal peritoneum have become obliterated by adhesion (Fig. 235).

[Fig. 236] shows this continuity of the descending and transverse mesocolon as a permanent adult condition in the macaque. The fold of transition between the two is seen at x in [Fig. 228]. It will be noticed that the ventral surface of the left kidney, caudad of the adherent pancreas, is covered by the primitive parietal peritoneum, corresponding to section in [Fig. 230].

RELATIONS OF SPLEEN AND OMENTUM IN MACACUS RHESUS.

The spleen in this animal has not contracted any extensive adhesions to the parietal peritoneum (the phrenico-lienal lig. of anthropotomy is not developed). It can be turned mesad so as to expose the lateral border and an adjacent segment of the ventral surface of the left kidney, as well as the dorsal surface of the tail of the pancreas at its tip, still covered by mesogastric peritoneum. Hence in the monkey the adhesion of the original vertebro-splenic segment of the mesogastrium, including the pancreas, to the primitive parietal peritoneum is less complete than in man.

MEDIAN ATTACHMENT OF DESCENDING MESOCOLON AND ITS RELATION
TO THE MESOCOLON OF THE SIGMOID FLEXURE IN THE MACAQUE.

Fig. 236.—Abdominal viscera of Macacus cynomolgus, Kra monkey. (Columbia University Museum, No. 1801.)

Fig. 236 shows the abdominal viscera, hardened in situ, of Macacus cynomolgus, the Kra monkey, in the ventral view and from the left side.

The great omentum is lifted up, the pancreas is adherent to the ventral surface of the left kidney, the caudal portion of which is covered by the primary parietal peritoneum, which can be exposed by turning the still free descending mesocolon mesad. The mesocolon retains its primitive attachment to the median line ventrad of the large prevertebral blood vessels. It is readily seen that adhesion between the left leaf of this free descending mesocolon and the parietal peritoneum down to the level of the iliac crest would produce the conditions found in the human adult, with an attached descending colon and a free sigmoid flexure; also that limited adhesion of the mesocolon of the sigmoid flexure to the parietal peritoneum would produce, as previously explained (cf. [p. 97]), the intersigmoid peritoneal fossa.

2. Ventral Mesogastrium and Liver.—The peritoneal reflections from the stomach to the liver, and the arrangement of the membrane in connection with the latter organ, remain for consideration.