138 THE ALIMENTARY SYSTEM. 



between rows of liver-cells, radiating from the intralobular 

 vein in the centre. They are so arranged that each liver-cell 

 abuts on at least one capillary. Through these capillaries 

 the blood passes from the portal vein to the hepatic vein, 

 coming into close relation with the liver-cells on the way. 

 The capillaries and the intralobular veins are lined with deli- 

 cate endothelium-cells which rest on the liver-cells. 



The bile-passages are exceedingly fine canals formed by 

 slight separations or grooves between adjacent liver-cells ; 

 short lateral blind branches sometimes also enter the bodies 

 of the cells themselves. These passages unite to form a fine 

 capillary network, which empties into the bile-ducts in the 

 interlobular septa. Each bile-capillary is separated from the 

 blood-capillaries by at least a portion of a liver-cell. These 

 passages collect the bile secreted by the liver-cells, and though 

 atypical they are the same in principle as the lumina of 

 tubular glands. In some animals, as the frog, the tubular 

 type is more apparent. 



The gall-bladder and hepatic, cystic, and common ducts 

 are lined with mucous membrane, consisting of simple long 

 columnar epithelium with intermingled goblet-cells, and sub- 

 epithelial connective tissue, in which mucous glands are 

 present. In the gall-bladder this coat forms intersecting rugae. 



Beneath the mucosa is a fibro-muscular coat, composed of 

 firm fibrous tissue containing involuntary muscle-cells. Out- 

 side of this coat, over the greater portion of the surface, is 

 an external serous or peritoneal covering. 



The bile in the gall-bladder is a dark opaque homogeneous 

 secretion, thick and viscid from the presence of mucin, and is 

 devoid of formed elements. 



The Pancreas. 



The pancreas (Fig. 59) is a racemose gland, which secretes 

 the pancreatic fluid. It is made up of secreting alveoli and 

 ducts, supported in connective or sustentacular tissue, which 

 divides it into lobes and lobules, and is supplied with blood- 

 vessels, lymphatics, and nerves. 



The sustentacular or connective tissue consists of an areolar 

 or fibrous capsule enveloping the gland ; of trabeculse or 



