264 



On the Vitelline Vein of the Cat 



three sides of the duodenum. The relation has changed in Fig. 4, 

 which is a section of a 7.6 mm. emhryo. Here the vein is purely laterad 

 to the intestine. 



There is no very great change in the relation of the duodenum to the 

 vitelline vein in an embryo of 13 mm. (Fig. 5) as compared with the 

 last stage (Fig. 4), except that the mesenchymal tissue Avhich forms 



Fig. .5. Embryo of 13 mm. 

 series 399. Section 460. 



Harvard Embryoloffical Collection. Transverse 



the walls of the gut is much thickened, its lumen is farther from the 

 vein, and the embryo is more developed in every respect. 



In the section of a 15 mm. embryo (Fig. 6) a pronounced change 

 has taken place. The vein may now be described as being in relation 

 to the mesentery of the duodenum, rather than in relation with the 

 walls of the intestine itself. 



Figs. 7 and 8 are sections of the duodenum, its mesentery, and the 

 vein, in embryos of 23.1 and 39 mm., respectively. The same extensive 



