202 MICROSCOPIC ANATOMY OF THE ORGANS. 



capillaries and end between the liver cells. At their extreme 

 ends the nerve filaments show varicosities (Berkley). 



The hepatic, cystic, and common bile ducts are the larger 

 channels concerned in the conduction of the bile to the intes- 

 tine. They consist of a mucosa, submucosa, and muscularis. 

 The mucosa consists of a single layer of columnar epithelium 

 and a tunica propria which contains small saccular mucous 

 glands and a few smooth muscle fibres. The submucosa is a 

 thin connective-tissue layer. The muscularis has been studied 

 in the whole extra-hepatic biliary system by Hendrickson. 

 According to him, all these ducts possess a distinct transverse 

 longitudinal and diagonal layer of smooth muscle arranged in 

 a somewhat plexiform manner. In the folds of the cystic duct 

 known as the Heisterian valve, muscle is also present. The 

 transverse fibres of the cystic duct run in a circular direction 

 in the valve, as though the wall at this level had been invagin- 

 ated. Most of the longitudinal fibres continue down the duct, 

 but a few turn into the valve almost at right angles. The 

 diagonal fibres do not at all enter the valve. At the entrance 



FIG. 157. 

 W 



K 



Macerated duodenal portion of the common bile duct of man. All of the intestinal coats 

 have been removed. 8, sphincter fibres. (Hendrickson.) X 5. 



of the common bile duct into the intestine at the duodenal 

 papilla an accumulation of the smooth muscle takes place, to 

 form a sphincter. Fig. 157, taken from Hendrickson 's work, 

 shows the arrangement of the muscle fibres in the sphincter. At 

 the junction of the duct of Wirsung (W) and the common bile 

 duct (B) there is a circular disposition of the fibres forming the 



