FOOD AND DIGESTION. 389 



into the ramifications of the portal vein, or into the capillary plexus of 

 the lobules which connect the inter- and intra-lobul&Y veins. 



The hepatic duct divides and subdivides in a manner very like that 

 of the portal vein and hepatic artery, the larger branches being lined 

 by cylindrical, and the smaller by small polygonal epithelium. 



The bile-capillaries commence between the hepatic cells, and are 

 bounded by a delicate membranous wall of their own. They appear to 

 be always bounded by hepatic cells on all sides, and are thus separated 

 from the nearest blood-capillary by at least the breadth of one cell (figs. 

 271 and 272). 



THE GALL-BLADDEB. 



The Gall-bladder (g.U. fig. 2G6) is a pyriform bag, attached to the 

 under surface of the liver, and supported also by the peritoneum, which 

 passes below it. The larger end, or fundus, projects beyond the front 

 margin of the liver; while the smaller end contracts into the cystic duct. 



Structure. The walls of the gall-bladder are constructed of three 

 principal coats. (I) Externally (excepting that part which is in contact 

 with the liver) is the serous coat, which has the same structure as the 

 peritoneum, with which it is continuous. Within this is (2) the fibrous 

 or areolar coat, constructed of tough fibrous and elastic tissue, with 

 which is mingled a considerable number of plain muscular fibres, both 

 longitudinal and circular. (3) Internally the gall-bladder is lined by 

 mucous membrane, and a layer of columnar epithelium. The surface 

 of the mucous membrane presents to the naked eye a minutely honey- 

 combed appearance from a number of tiny polygonal depressions with 

 intervening ridges, by which its surface is mapped out. In the cystic 

 duct the mucous membrane is raised up in the form of crescentic folds, 

 which together appear like a spiral valve, and which minister to the 

 function of the gall-bladder in retaining the bile during the interval of 

 digestion. 



The gall-bladder and all the main biliary ducts are provided with 

 mucous glands, which open on the internal surface. 



FUNCTIONS OF THE LlVEE. 



The function of the liver in connection with digestion is to secrete 

 the bile, and may be now considered. The other functions in connec- 

 tion with the general metabolism of the body, and particularly its gly- 

 cogenic function, will be discussed later on. First of all it will be as 

 well to take the composition and functions of the bile, and afterward to 

 discuss its mode of secretion. 



