108 PRACTICAL MICROSCOPY. 



The hepatic duct is also seen emerging from the transverse fissure. 

 (For sake of clearness, we will trace it from without inward.) It fol- 

 lows the courses of the portal vein with the hepatic artery. Wherever 

 in a section of the organ the portal is divided, the artery and duct 

 will also appear. Bound together with connective tissue, the trio 

 reach the walls of the lobules. The ducts now penetrate the lobules 

 and break up into an exceedingly minute plexus the bile capillaries. 

 This plexus properly begins in the lobules and drains the bile as 

 formed, passing it into the ducts in the opposite direction of the por- 

 tal blood current, 



THE PORTAL CANALS. 



If it were possible to grasp the vessels as they are found emerging 

 at the transverse fissure, the portal vein, hepatic artery, and hepatic 

 duct, and to forcibly tear them, with their supporting connective tis- 

 sue, out of the liver, a series of channels or canals would thereby be 

 formed. A portal canal, then, is the space in the liver occupied by 

 the portal vein, the hepatic artery, the hepatic duct, and the contiguous 

 connective tissue. Frequently more than one specimen of each vessel 

 is to be seen in the canals. There may be two or three veins, and as 

 many arteries and ducts, associated in a single portal canal. Lym- 

 phatic chinks are also abundant in this connective tissue. 



From what has been said, it will be understood that a vessel found 

 by itself in this organ must be either a centred or an hepatic vein; and 

 these are easily distinguished, as the former are within, while the lat- 

 ter are without the lobules and in the connective-tissue framework. 

 On the other hand, a group of vessels ivill indicate a portal canal? 

 with its large and thin-walled vein, the small thick-walled artery, and, 

 intermediate in size, the duct. 



THE LOBULAR PARENCHYMA. 



The lobules consist of two capillary plexuses, one containing blood 

 and the other bile. In the meshes of this network, the hepatic cells 

 are located. 



The blood capillaries, although extremely tortuous, have a general 

 direction of convergence toward the central veins. This is best seen 

 when the lobules have been divided in a vertical direction. 



The bile capillaries are among the smallest canals found in vascular 

 tissues, having a diameter of one-twelve thousandth of an inch. They 

 pursue a direction in the human liver, as a rule, at right angles to 

 the course of the blood capillaries, and are not demonstrable, except 



