PHYSIOLOGICAL ANATOMY OF THE LIVER. 



435 



The hepatic veins differ somewhat in their structure from other portions of the venous 

 system. Their walls are thinner than those of the portal veins, they are not enclosed 

 in a sheath, and they are very closely adherent to the hepatic tissue. It is this provision 

 which makes the force of aspiration from the thorax so efficient in the circulation in 

 the liver. Here, indeed, a force added to the action of the heart is specially necessary; 

 for the blood is passing into the liver through a second capillary plexus, having already 

 been distributed in the capillaries of the alimentary canal and other abdominal organs, 

 before it is received into the portal vein. It has also been noted that the hepatic veins 

 possess a well-marked muscular tunic, very thin in man, but well-developed in the pig, 

 the ox, and the horse, and composed of unstriped muscular fibres interlacing with each 

 other in every direction. 



In addition to the blood-vessels just described, the liver receives venous blood from 

 vessels which have been called accessory portal veins, coming from the gastro-hepatic 

 omentum, the surface of the gall-bladder, the diaphragm, and from the anterior abdominal 

 walls. These vessels penetrate at different portions of the surface of the liver, and they 

 may serve as derivatives, when the circulation through the portal vein is obstructed. 



Structure of a Lobule of the Liter. Each hepatic lobule, bounded and more or less 

 distinctly separated from the others by the inteiiobular vessels, contains blood-vessels, 

 radicles of the hepatic ducts, and the so-called hepatic cells. The arrangement of the 

 blood-vessels has just been described ; but, in all preparations made by artificial injec- 

 tion, the space occupied by the blood-vessels is exaggerated by excessive distention, and 

 the difficulties in the study of the relations of the ducts and the liver-cells are thereby 

 much increased. As the important problem in the minute anatomy of the lobules has 

 been the relations of the cells to the radicles of the bile-ducts, we shall first take up the 

 structure of the cells. 



Hepatic Cells. If a scraping from the cut surface of a fresh liver be examined with a 

 moderately high magnifying power, the field 

 of view will be found filled with numerous 

 rounded, ovoid, or irregularly polygonal cells, 

 measuring from T3 Vjr to -j^Vo" of an inch in 

 diameter. In their natural condition, they are 

 more frequently ovoid than polygonal; and, 

 when- they have the latter form, the corners 

 are always rounded. These cells present one 

 and sometimes two nuclei, sometimes with and 

 sometimes without nucleoli. The presence of 

 numerous small pigmentary granules gives to 

 the cells a peculiar and characteristic appear- 

 ance; and, in addition, nearly all of them 

 contain a few granules or small globules of fat. 

 Sometimes the fatty and pigmentary matter is 

 so abundant as to obscure the nuclei. The 

 addition of acetic acid renders the cells pale 

 and the nuclei more distinct. By appropriate * 



reagents, animal starch (probably glycogenic matter) has been demonstrated in the sub- 

 stance of the cells. 



Arrangement of the Bile-ducts in the Lolules.In describing the plexus of origin of 

 the biliary ducts, we shall not discuss the views of Kiernan, Leidy, Beale, and others, as 

 recent researches have conclusively shown that these were entirely erroneous. Late 

 researches have shown that the following is probably the true relation of the ultimate 

 ramifications of the bile-ducts in the lobules to the hepatic cells : 



In the substance of the lobules, is an exceedingly fine and regular net- work of vessels, 



FIG. 131. Liver-cells, from a Jivman, fatty lirer. 

 (Funke.) 



