DEVELOPMENT OF THE ALIMENTARY TUBE AND APPENDED ORGANS. 351 



between the parenchyma of the gland and the blood vessels, has not been 

 clearly and completely demonstrated. In young embryos the branches of the 

 hepatic veins are surrounded by comparatively little connective tissue. The 

 branches of the portal vein are surrounded by a considerable amount which 

 subdivides the liver into lobules but not in the same manner as in the adult. 

 The trabecular possess no radial character and there are several so-called central 

 veins in each lobule. The changes by which these primary lobules are sub- 

 divided into the permanent ones do not take place until after birth. The 

 branches of the portal vein, with the surrounding connective tissue, invade the 



Fig. 315. — Sections of the liver of (A) a human foetus of 6 months and (B) a child of 4 years. 



Toldt and Zuckerhandl. McMurrich. 



be, Bile "capillary"; e, erythroblast; he, hepatic cylinder (in A), cord of liver cells (in B). 



primary lobules and divide them into a number of secondary lobules, corre- 

 sponding to the original number of central veins. At the same time the hepatic 

 cords (which have been formed meanwhile) become arranged radially around 

 the central veins in the characteristic manner. The hepatic artery grows into 

 the liver secondarily and its branches follow the course of the branches of the 

 portal vein. 



Degeneration of the liver cells occurs in the region of the left triangular liga- 

 ment, the gall bladder and the inferior vena cava. The bile ducts may, how- 

 ever, withstand the degenerative processes and persist as the vasa aberrantia of 

 the liver. The cause of the degeneration is possibly the pressure brought to 

 bear by other organs. 



The Development of the Pancreas. 



The epithelium of the pancreas, like that of the liver, is a derivative of the 

 ' entoderm. It arises from two (or three) separate anlagen, one dorsal and one 

 23 



