114 



Georae Heuer. 



duct is seen extending into the villus. The arterj and vein are sbo\vn 

 in the drawing. 



There are, then, in the mucous membrame of an embryo 9 cm. 

 long all the essential structures which go to make up the lymphatic 

 plexuses as found in the mucosa and submucosa of the adult, and 

 it is by the growth of these parts that the latter are derived. 



Fig. 14. — Cleared specimen of a loop of the small intestine from an embryo 

 pig 16 cm. long to show the mesenteric vessels with their valves, the large 

 meshed submucosal plexus, the deeper, closer-meshed mucosal plexus, and the 

 central lacteals. 



In Fig. 13 is shown an incomplete injection of the duodenum to 

 show the very large ducts at the root of the mesentery, the fact that 

 the vessels follow the artery in the mesentery, and thirdly, that 

 there are beginning tertiary lymph nodes along the ducts in the 

 mesentery. In Figs. 14 and 15 are shown injected lymphatics in 



