THE LIVER 189 



the bile secreted by tlie hepatic cells. Each hepatic cell uia\' have 

 more than one bile capillary into which it cHscharjijes bile, but they 

 occur only between adjoininjj surfaces of cells and not alonjj the 

 free surfaces which adjoin the blood sinusoids. These capillaries 

 form a branching network and join those of adjoining hepatic cords 

 to carry the bile outward toward the periphery of the l()l)ule. At 

 the periphery of the lobule they collect into small bile ducts in the 

 interlobular septa. These interlobular bile ducts have walls formed 

 of flat or cuboidal e])ithelium and coalesce to form larger ducts 

 following the course of the portal vein and hepatic artery through 

 the septa. With increasing size of the bile vessels, the epithelium 

 of their wall changes to tall columnar which is surrounded by a 

 coat of connective tissue and scattered longitudinal smooth muscle 

 cells. The larger bile ducts from each lobe empty into a larger 

 hepatic duct that in turn joins the common bile duct leading into 

 the duodenum. 



The three vessels coursing close together through the connective- 

 tissue septa of the liver, i. e., a branch of the he])atic artery, a 

 branch of the portal vein, and a bile duct, form the so-called portal 

 canal peculiar to the liver. The vein is the largest, the bile duct 

 is second in size, and the artery is the smallest vessel of the three. 



As a gland the liver is peculiar in passing its secretions peripher- 

 alh' to the collecting ducts and, although the hepatic cells are only 

 of one type, they are presuma})ly equally ca])able of many different 

 functions. Moreover, the blood com-ses not outward from a center, 

 but in toward the center of each lobule where it is collected into 

 efferent veins that follow at first a course different from the small 

 afferent vessels and ducts of the gland. The amount of connective 

 tissue varies in different animals, being particularly well represented 

 in the pig liver, where the interlobular connecti\'e tissue clearly 

 marks the boundaries of the lobules. The arrangement of the 

 hepatic cells is unique as regards their relation to sinusoids, and 

 the bile capillaries are mere troughs between the adjacent faces of 

 two cells. 



The liver is associated with the production of l)ile which is carried 

 to the duodenum, where it is mixed with food and ])ancreatic en- 

 zymes. Part of the bile consists in secretion products from the 

 liver cells, and in part it consists of excretions which the li\er cells 

 have removed from the blood. Apparently liAcr cells are able to 

 excrete foreign substances that have entered the blood. I3ile acids 

 produced by the liver cells take j^art in the absorption of fats from 



