472 LIVER. [CHAP, xxxni. 



and forwards; it terminates in the cystic duct, which is about an 

 inch in length. The hepatic duct, leaving the liver by the trans- 

 verse fissure, passes downwards, and soon joins the cystic duct at 

 an acute angle, to form the ductus communis choledochus, which is 

 about three inches in length, and lies between the layers of the 

 gastro-hepatic omentum. After coming into close proximity with 

 the pancreatic duct, the common duct enters the coats of the 

 intestine with the latter, and passes obliquely between them for 

 three-quarters of an inch. The ducts open by an orifice common 

 to both at the junction of the descending and transverse portions 

 of the duodenum. The mucous membrane of the gall bladder is 

 thrown into reticulated folds, which form the boundaries of nu- 

 merous polygonal depressions, so that upon its internal surface it 

 presents a honeycombed appearance. It is highly vascular, and is 

 covered with columnar epithelium. The folds are prolonged into 

 the cystic duct, where they are arranged in a crescentic manner, 

 their general direction being that of a spiral, and they have been 

 compared to a spiral valve. The peculiar arrangement of the 

 vessels of the gall bladder has been already referred to. The cystic 

 artery is derived from the right division of the hepatic, and the 

 veins empty themselves into the vena portae. The lymphatics are 

 very numerous. The greater part of the thickness of the walls of 

 the gall bladder is composed of fibrous tissue, but there also exists 

 a thin layer of delicate muscular fibre cells, which take partly a 

 longitudinal and partly a transverse direction. The human gall 

 bladder is capable of containing about an ounce of fluid, but it 

 undergoes great alterations in volume, and in it the bile becomes 

 inspissated, and probably undergoes other changes. 



This viscus is absent in many genera of fishes ; in pigeons, toucans, and 

 some other birds; in the elephant, stag, horse, and tapir; but it is present in 

 the ox, sheep, and antelope. It is always found amongst reptiles. The reason 

 of its absence in the animals above alluded to is not yet satisfactorily 



explained. 







Hepatic Vein. The branches of the hepatic vein run in channels, 

 which are situated between the portal canals (Fig. 217), and in 

 consequence of the small quantity of areolar tissue surrounding 

 the hepatic vein, the bases of the adjacent lobules are in contact 

 with it, so that when a branch of the hepatic vein is cut across, it 

 does not collapse, but remains open. The small twigs which 

 collect the blood from the lobules surrounding the trunk of 

 the vein open at once into it, except in the case of the largest 

 branches, where the coats are very thick. This arrrngement is 

 shown in Fig. 225, after Mr. Kiernan. In this drawing, the open- 



