VI.J THE LIVER. 179 



60tli hour as a couple of diverticula one from either 

 side of the duodenum immediately behind the stomach 

 (Fig. 60, I). These diverticula are of course lined by 

 hypoblast. The right one is, in all cases, from the first 

 longer, but of smaller diameter than the left. Situated 

 a little behind the heart, they embrace between them 

 the two vitelline veins forming the roots of the meatus 

 venosus. 



The diverticula soon give rise to numerous hollow 

 branches or processes, which extend into the surround- 

 ing mesoblast. 



Towards the end of the third day there may further 

 be observed in the greatly thickened mesoblastic invest- 

 ment of either diverticulum a number of cylindrical 

 solid cords of hypoblast which are apparently out- 

 growths from the hypoblast of the branches of the di- 

 verticula. These cylinders rapidly increase in number, 

 apparently by a process of sprouting, and their some- 

 what swollen peripheral extremities come into contact 

 and unite, And thus, about the ninetieth hour, a sort 

 of network of solid thick strings of hypoblastic cells is 

 formed, the mesoblast in the meshes of the network 

 becoming at the same time largely converted into 

 blood-vessels. Each diverticulum becomes in this way 

 surrounded by a thick mass composed partly of solid 

 cyHnders, and to a less extent of hollow processes, con- 

 tinuous with the cylinders on the one hand, and the 

 main diverticulum on the other, all knit together with 

 commencing blood-vessels and unchanged mesoblastic 

 tissue. Between the two masses runs the now fused 

 roots of the meatus venosus with which the blood- 

 vessels in each mass are connected. 



12—2 



