542 



SPECIAL HISTOLOGY. 



from one or other set of vessels, at least 3, usually 45, smaller vessels of 

 1-120-1-60 of a line, which Kiernan calls vence inter lob ulares. Such a 

 vein, however, is never distributed to only one hepatic islet, but always 

 to two, or even three. Their ultimate branches, the rami lobulares of 

 Kiernan, 10-20 in number, enter the neighboring hepatic islets, usually 

 at a right angle, and divide immediately into the capillary network, 

 without becoming, in man, directly united with one another. In fact, 

 the branches of the portal vein nowhere anastomose, but are connected 

 merely by the finest vascular network of the organ. 



Fiar. 222. 



Fiur. 223. 



The capillary network of the islets (Fig. 222) completely fills the 

 interspaces of the hepatic cell-network, so that the secreting parenchyma 

 consists actually of only two elements, the hepatic cells and the capilla- 

 ries. Exactly as the hepatic cell-network is continuous through the 

 entire liver, though being interrupted by the biliary ducts which pass off 

 and the vessels which enter, at regular intervals, it is divided into sepa- 

 rate, very minute areace so the capillary network of the bloodvessels 

 passes from one hepatic islet to another, but is nevertheless discontinuous 

 in certain spots. The diameter of the capillaries is, in general, some- 

 what less than that of the hepatic cell-network, though relatively con- 

 siderable; in man it is, on the average, 0-004-0-0055, 0-002-0-01 of a 

 line, in extreme instances ; the wide vessels being more especially found 

 in the neighborhood of the afferent and efferent veins, the narrowest in 



FiG. 222. Hepatic cell-network and its capillaries, magnified 350 diameters ; from the 

 Pig. Spaces are purposely left here and there between the cells and capillaries, which do 

 not exist in nature. 



FIG. 223. Segment of a very successful injection of the hepatic veins of the Rabbit, 

 magnified 35 diameters. One vena intralobularis is visible in its entire course, but only the 

 radicles of the other. The capillaries of the lobules partly coalesce, and, in one place, two 

 venous radicles do so. 



