The primitive dorsal mesentery, as already stated, passes as a thin double-layered membrane between the ventral surface of the vertebral column and the dorsal border of the stomach, which, as we will presently see, becomes during the later stages of development the caudal (lower) margin or greater curvature.
It will be seen that the embryonic differentiation of the intestinal tract into successive segments justifies the application of a terminology based on this differentiation to the corresponding portions of the primitive common dorsal mesentery.
Thus the proximal portion extending between the vertebral column and the dorsal border or greater curvature of the stomach becomes the mesogastrium; we differentiate this portion still further as the “dorsal mesogastrium” to distinguish it from a “ventral mesogastrium” which we will presently encounter in considering the development of the liver and the connected peritoneum.
In the same way the section of the primitive common dorsal mesentery attached to the duodenal loop becomes the mesoduodenum, that connected with the mobile part of the small intestine (jejuno-ileum) the mesentery proper, while the portion passing to the colon forms the mesocolon, to be subsequently still further subdivided, after the different segments of the large intestine have become mapped out, as the ascending, transverse and descending mesocolon, the mesosigmoidea and the mesorectum.
In tracing the development of the adult human peritoneum it is well to consider certain stages, which we will find illustrated by the permanent conditions presented by some of the lower vertebrates:
These stages comprise:
(a) Changes in the position of the stomach.
(b) Changes in the direction and extent of the dorsal mesogastrium.
(c) Development of the pancreas and spleen in connection with the mesogastrium.