564 THE HUMAN EMBRYO. 



placenta by the allantoic veins ; and it almost certainly acts as 

 an important excretory organ during embryonic and foetal life. 



The brown, or greenish-brown, mass known as meconium, 

 which occurs in the small intestine from the third to the fifth 

 month, and lower down, in the large intestine and rectum, during- 

 the later months of pregnancy, contains bile in considerable 

 quantity, as well as mucus, and epithelial and other debris. 



11. The Pancreas. 



The pancreas arises, towards the close of the fourth week, as a 

 dorsally directed diverticulum from the duodenum, almost oppo- 

 site the opening of the bile-duct (Figs. 233 and 234, P), and lying 

 in the thickness of the mesentery which attaches the duodenum 

 to the dorsal body- wall. The pancreas grows rapidly, giving off 

 lobed offshoots, from which the acini and their ducts are formed. 

 The original diverticulum from the duodenum persists as the 

 pancreatic duct ; it at first opens a little distance from the 

 bile-duct, but ultimately the two ducts lie close alongside each 

 other, and open into the duodenum by a single orifice. 



12. The Mesentery. 



The mesentery is the thin vertical sheet of mesoblast which 

 slings the stomach and intestine to the body-wall. The relations of 

 the mesentery are at first extremely simple, but as the intestine 

 lengthens, and especially as it becomes thrown into convolutions, 

 they become greatly complicated. The attachment of the dorsal 

 border of the mesentery to the body-wall remains comparatively 

 unmodified throughout life, though at certain places oblique or 

 transverse lines of attachment are acquired in addition to, or in 

 place of, the original simple longitudinal attachment. 



The part of the mesentery which attaches the stomach to the 

 body-wall, commonly spoken of as the mesogaster, undergoes 

 special modification. The stomach originally lies lengthways 

 along the body (Fig. 233, Mg, and 243), the mesogaster being at- 

 tached along the border which will afterwards become the greater 

 curvature of the stomach, and the pancreas (Fig. 233, P) lying 

 in the thickness of the mesogaster near its posterior limit. 

 When the stomach shifts its position, and becomes placed trans- 

 versely across the body (Fig. 236), its original left side becomes 

 ventral, and its right side dorsal ; while the mesogaster remains 

 attached along what is now the posterior border of the stomach. 



