263 



Thus the portal canals are formed, and after birth they may anasto- 

 mose. The increase of connective tissue does not extend into the 

 lobules. Between the hepatic cylinders, sinusoids persist throughout life. 

 The so-called central veins are large vessels which replace several 

 smaller ones (Maurek)-). In structure they remain sinusoidal rather 

 than venous. 



In all glands, including the liver, the ducts are the axial structures. 

 The liver differs from others in possessing anastomosing lobules and 

 in the absence of connective tissue at their periphery. Both of these 

 features are due to its sinusoidal development. When the bile ducts 

 are injected they appear as a net 

 spreading evenly from the portal canal 

 toward all the surrounding central 

 veins. These injections mark out 

 lobules with portal canals at their 

 centres , and central veins at the 

 periphery. Such have been described 

 by ScYMONOWicz as "secretory units". 

 They are the portions of the liver 

 comparable with the lobules of other 

 glands. 



The usual description of the 

 mammalian liver on the basis of 

 lobules with veins at their centres is 

 no longer defensible. It necessitates 

 arranging the bile ducts in a manner 

 not found by injection. (Compare 

 Cadiat's correct figure of the injected 

 ducts, in Schäfer's "Essentials of 

 Histology", with the diagrams of 

 Stöhr and Scymonowicz, which differ 

 from each other and are both in- 

 correct.) Moreover it is not consistent 

 with the embryological history of the 



organ. Von Ebner ^) states that "the livers of animals which present 

 sharply defined lobules (polar bear, pig) are of the greatest importance in 

 understanding the structure of this organ". On the contrary, this con- 



1) Handbuch der Entvi^ickelungslehre der Wirbeltiere, Bd. 2, Abt. 1, 

 p. 198. Jena 1902. 



2) A. Koelliker's Handbuch der Gewebelehre, Bd. 3, p. 214. 

 Leipzig 1902. 



Fig. 2. Rabbit embryo of 5 mm, 

 12 days. Harvard Embryological Col- 

 lection 104, Section 326. To show the 

 invasion of the vitelline vein, V. V., by 

 the trabeculae of the liver, Li. Int. 

 Intestine. ' P. C. Pericardial cavity. 

 K C. Cardinal vein. V. Urn. Umbilical 

 vein. X 27 diams. 



