THE DIGESTIVE AND RESPIRATORY SYSTEM 293 



It is of interest in this connection to trace the changes in the 

 mesentery of this region, more precisely termed the mesogas- 

 trium, as they appear in successive stages in the mammalian 

 embryo which are undoubtedly of historical significance (Fig. 

 81). The formation of the initial curvature to the left natu- 

 rally broadens the corresponding part of the mesogastrium, an 

 effect still further increased by the lateral torsion of the entire 

 stomach. At this point the widened mesentery comes under 



ir 



IV 



FIG. 81. Development of the peritoneal folds and of the windings of 

 the alimentary canal in the human embryo. [From HERTWIG, Figure I 

 after His; Figure II after TOLDT.] 



Figure I shows the. spindle-shaped stomach, the lung anlagen, and the beginning 

 of the liver in the form of a median diverticulum; in Figure II the peritoneum is 

 shown, with pancreas and spleen; figures III and IV show the development of the 

 omentum and the lesser peritoneal cavity. 



the influence of the spleen, which develops within it and by its 

 weight produces a fullness which sags down behind (dorsal 

 to) the lesser curvature, while attached to the greater; and 

 the continuation of this tendency causes the free lower fold 

 of the bag-like extension to hang down behind the contour 

 of the stomach. 



This fold is the greater omentum (omentum mafus), which, 

 as all mesenteries are essentially double, consists of four layers 



