Franklin Dexter 



265 



growth has continued, and now at 39 mm. the gut is found at an appre- 

 ciable distance from the vein. The continued growth of the duodenum 

 to the right, together with the immobility of the vein, fully accounts for 

 the change in relation to the duodenum and vitelline vein as seen in 

 the youngest embryo, and in the cat at birth. 



We have already seen (Fig. 1) the relations of the vitelline artery 



Mes 



SMA 



LUV 



Fig. 0. Embryo of 15 mm. Harvard Embryological Collectiou. Transverse series 

 436. Section 527. 



throughout its entire extent. Fig. i is taken from the same series, 

 the twelfth section cephalad to it. It shows remarkably clearly the 

 course of the vein from the yolk sac to the duodenum. The vein is 

 ■seen to be unconnected with any mesentery. It lies absolutely isolated 

 and alone until it reaches the mesentery of the duodenum. 



One can easily identif}^ either in this section, or in one made at right 

 ang-les to the intestine, its endothelial lining, Avhich is surrounded by a 



