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 oesophageal entrance is at the highest or cephalic point of the organ, while the pyloric transition to the small intestine occupies the distal caudal extremity. 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.