[Illustration: FIG. 236.--Abdominal viscera of _Macacus cynomolgus_, Kra monkey. (Columbia University Museum, No. 1801.)] MEDIAN ATTACHMENT OF DESCENDING MESOCOLON AND ITS RELATION TO THE MESOCOLON OF THE SIGMOID FLEXURE IN THE _MACAQUE_. 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. Certain complicated adult conditions, encountered in this part of the abdominal cavity, make it desirable to arrange the subject for purposes of study under the following subdivisions: I. The development of the liver and of its vascular system, and the significance of the adult circulation of the liver and of the foetal remnants connected with the organ. II. The anatomy of the ventral mesogastrium and the changes produced in the arrangement of the membrane by the development of the liver. =I. A. Development of the Liver.=--The liver, like the pancreas, is developed from the duodenum as an outgrowth from the hypoblast lining the enteric tube. As we have previously noted, the first outgrowth of the hepatic diverticulum is closely associated with the distal pancreatic outbud; in fact the latter arises as a derivative from the hepatic duct rather than as a distinct outbud from the intestinal tube. (This close association of the hepatic duct with the pancreas is well seen in the arrangement of the concealed pancreas of some teleosts (cf. p. 117, Fig. 196).) In point of time the liver is the first accessory structure to develop by budding from the primitive alimentary canal, the pancreas and lung following. [Illustration: FIG. 237.--Longitudinal section of an embryo of _Petromyzon planeri_, four days old. (Minot, after Kupffer.)]