HISTOGENESIS OF THE LIVER 



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while in birds and mamfnals the 'Vorleber' is a precursor of 

 that organ. Also the selachian mesenchymal mass lies in the 

 dorsal and posterior part of the liver along its free upper surface, 

 while the 'Vorleber' lies anteriorly and is broadly connected with 

 the dorsal wall of the coelom. Ziegler ('88) showed long ago that 

 the mesenchyma of the intestine in selachians arose from two 

 longitudinal zones of proliferation from the splanchnic mesoderm. 

 One of these zones lies above the archenteron and the other 



Fig. 10 A comparison of Ziegler's figure: A, of the mesenchymal tissue in 

 the trunk region of a selachian embryo with a semi -diagrammatic figure; B, show- 

 ing the origin of the mesenchyma in the hepatic region of an Acanthias embryo. 



ventral to it. The method of development of the hepatic mesen- 

 chyma indicates that these dorsal and ventral zones of pro- 

 liferation extend forward into the liver region as well and remain 

 distinct for a considerable period even after the liver has separated 

 from the gut above it. A comparison of a semi-diagrammatic 

 figure of a cross-section through the hepatic region with Ziegler's 

 diagram of a similar section through the middle of a trunk seg- 

 ment shows the essential agreement in the origin of the splanchnic 

 mesenchyma in the two regions (fig. 10). 



