ANATOMY OF THE PERITONEUM IN THE SUPRA-COLIC COMPARTMENT OF THE ABDOMEN.
We have already seen that the transverse colon and mesocolon effect a general division of the adult human abdominal cavity into a cephalic supra-colic compartment, situated between the diaphragm and the level of the transverse colon and mesocolon, comprising in general the hypochondriac and epigastric regions, and a larger caudal infra-colic space which includes the entire rest of the abdominal cavity and is continued caudad into the pelvic cavity. The arrangement of the peritoneum and viscera in this latter space has just been considered. The fact will be recalled that the second or descending portion of the duodenum, passing dorsad of the hepatic colic flexure, forms so to speak the visceral connection between the portions of the alimentary tube situated in the supra-colic compartment and those situated in the infra-colic space. The fixation of this segment of the duodenum and its consequent secondary retroperitoneal position in the adult human subject masks this continuity of the alimentary canal to a certain extent so that it requires more than a superficial examination in order to trace correctly the course of the duodenum from the pylorus to the duodeno-jejunal angle, dorsad of the colon, root of transverse mesocolon and mesentery, and under cover of the secondary parietal peritoneum.
We have now to turn our attention to the viscera contained in the cephalic or supra-colic compartment of the abdomen and to consider the disposition of the serous membrane investing them and connecting them with each other and with the abdominal parietes.
The visceral contents of the supra-colic compartment comprise the liver, pancreas, spleen, stomach and the proximal portion of the duodenum, including the hepatic angle and the supra-colic part of the descending duodenum. Less directly the cephalic portions of the right and left kidney and the corresponding suprarenal capsules belong to this visceral group.
In this region of the abdomen we meet with the most extensive modifications of the primitive dorsal peritoneal membrane, producing conditions which, considered without reference to development and comparative anatomy, are complex and difficult of comprehension. These changes lead to the formation of the so-called “lesser sac,” a term which in some respects is unfortunate as it implies a more complete degree of separation from the general peritoneal cavity or “greater sac” than actually exists.
In order to clearly understand the adult arrangement of the peritoneum in this region it is advisable to consider the subject in two distinct subdivisions, dealing successively with the two cardinal facts which contribute to effect the change from the simple primitive to the complicated adult condition.
These two main elements are:
1. Developmental changes in the position of the stomach, alterations in the disposition of the proximal part of the primitive dorsal mesentery attached to the stomach, and the development of pancreas and spleen in connection with this membrane.
2. The development of the liver and the successive stages in the production of the final adult vascular and serous relations of this organ.
1. Stomach and Dorsal Mesogastrium.—We have already considered the early stages in the differentiation of the stomach from the primitive intestinal tube of uniform caliber ([p. 40]). It will be recalled that the stomach at a certain period, while it already presents the main structural features familiar in the adult organ, occupies a vertical position in the abdominal cavity, turning its concave margin (lesser curvature) ventrad, while the convex dorsal border (greater curvature) is directed toward the vertebral column, being attached to the same by the layers of the proximal part of the primitive dorsal mesentery. At this time the stomach presents right and left surfaces, and the œsophageal entrance is at the highest or cephalic point of the organ, while the pyloric transition to the small intestine occupies the distal caudal extremity.