HISTOGENESIS OF THE LIVER 



289 



same rate and the development of the vascular supply of the 

 organ is closely related to its growth. Such a study, however, 

 does give us some rough approximations which may be of value. 



A study of table 2 brings out clearly the three stages in the 

 vascularization of the liver in Acanthias. The first stage found 

 in an embryo between 12 and 20 mm. in length is one in which 

 the tubules are growing with great rapidity and the sinusoids 

 are only cleft like endothelium lined spaces (figs. 14 A and B). 

 It is only in the lateral lobes of the liver where the hepatic and 

 the hepatic-portal veins unite in large sinuses that the vascular 

 percentage of the organ is high. During the latter part of this 

 period tubule anastomoses are- forming in large number. With 

 anastomosis the vascular supply of the organ increases with the 

 greatest rapidity and the tubules, taking on the form of slender 

 cylinders, are separated by very large vascular spaces. This 

 phase, which is inaugurated rather suddenly, continues while the 

 embryo grows from a length of about 20 mm. to a length of 



TABLE 2 

 Measurements of the hepatic vascular spaces in Acanthias embryos 



' T.a., total area of cross section in square mm.; V.a., area of vascular spaces in square mm.; V.%, 

 percentage of total area occupied bj' vascular spaces. 



