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arterio-venous connection is the source of capillaries. They branch 

 freely over the surfaces of organs, lying in an abundant connective 

 tissue. In their double origin from both an artery and a vein, and in 

 their relation to connective tissue they ditfer from sinusoids. 



These features are represented in the diagram. Fig. 1. On the 

 right is the pancreas with its capillaries; on the left the liver and 

 sinusoids. If the gland tissue of the pancreas were entirely removed, 

 artery, vein, and capillaries would remain unchanged; but if the hepatic 



vci 



V Ar 



Fig. 1. Diagram showing on the right, the pancreas and its capillaries; on the left, 

 the liver and its sinusoids. The connective tissue is represented by dots. Ar. Artery. 

 Int. Intestine. V. Vein. V.C.I. Vena cava inferior. V.P. Portal vein. 



tubules were withdrawn, their place would be indicated only by a venous 

 sinus, a dilated and subdivided portion of a single vein. As will be 

 shown presently, the gross differences in structure between liver and 

 pancreas are due to their contrasting forms of blood supply. 



It is the purpose of this paper to describe the development and 

 fate of the sinusoids in three organs; first, the liver; second, the 

 Wolffian body; and finally, the heart. 



Liver. 



The liver invades and subdivides the vitelline veins, into which the 

 umbilical veins also come to empty. It has consequently a sinusoidal 

 circulation. This process is represented in the cross section, Fig, 2. 

 The afferent portal vein and the efi'erent vena cava inferior, being 

 parts of the vitelline vein, are found on opposite sides of the liver, 

 and communicate with one another through a network of hepatic sinu- 

 soids as shown in the diagram. Fig. 1 . At first the liver contains the 

 slightest possible amount of connective tissue. This is later increased 

 by a development which follows the vena cava, and transforms certain 

 of its tributary sinusoids into veins. Another and more extensive in- 

 growth of connective tissue occurs along the bile ducts and portal vein. 



