1062 



THE ORGANS OF DIGESTION. 



(3) The Ducts. Having shown how the blood is brought into intimate relation 

 with the hepatic cells in order that the bile may be secreted, it remains now only 

 to consider the way in which the secretion, having been formed, is carried away. 

 Several views have prevailed as to the mode of origin of the hepatic ducts ; it 

 seems, however, to be clear that they commence by little passages which are 

 formed between the cells, and which have been termed intercellular biliary pas- 

 sages or bile-canaliculi (Fig. 673). These passages are merely little channels or 

 interspaces left between the contiguous surfaces of two cells or in the angle where 

 three or more liver-cells meet, and it seems doubtful whether there is any delicate 

 membrane forming the wall of the space. The channels thus formed radiate to 

 the circumference of the lobule, and, piercing its wall, form a plexus (interlobular') 

 between the lobules. From this plexus ducts are derived which pass into the por- 

 tal canals, become enclosed in Glisson's capsule, and, accompanying the portal 

 vein and hepatic artery (Fig. 674), join with other ducts to form two main trunks, 

 which leave the liver at the transverse fissure, and by their union form the hepatic 

 duct. 



Structure of the Ducts. Those in the interlobular spaces have walls of con- 

 nective tissue lined by columnar epithelium. They probably contain muscle-cells 



FIG. 675. Blind tubules of the bil- 

 iary ducts of a horse. (Sappey.) 



FIG. 676. Liver tissue over the posterior surface of the vena 

 cava inferior, with injected vasa aberrantia. (Henle.) 



arranged longitudinally and circularly. As they lie in the lobule the columnar 

 epithelium is very short and flat and the lumen very small. The bile-canaliculi 

 open directly into them, liver-cells abutting against the epithelium. The ducts in 

 the portal canals are larger, and present numerous openings on the inner surface, 

 sometimes arranged in two rows. Sappey considers them the orifices of mucous 

 glands (Fig. 675), and compares their appearance to that of the vegetable pai-asites. 

 Their function is much discussed, arid at present they are regarded only as tubular 

 recesses. They occasionally anastomose, and from their sides saccular dilatations 

 are given off. 



Sometimes certain parts of the liver gradually atrophy or completely disappear, 

 while the corresponding biliary ducts remain and, on the contrary, become hyper- 

 trophied. They are called vasa aberrantia. They are not found in the foetus or 

 child, are not rare in the adult, and are most frequent in old age. Accompanying 

 them are all the other vessels which supplied the part, branches of the portal vein, 

 hepatic vein, and artery. They are situated at either extremity of the liver, most 

 often in the left lateral ligament, at the attachment of the falciform, or in the posi- 

 tions of atrophied "bridges," as over the left longitudinal fissure or vena cava 

 (Fig. 676). They present certain common characteristics. All communicate with 



