748 



ORGANS OF DIGESTION. 



left lobe; these unite, and pass downwards and to the right for about an inch 

 and a half, to join at an acute angle with the cystic duct, and so form the ductus 

 communis choledochus. 



The cystic duct, the smallest of the three biliary ducts, is about an inch in 

 length. It passes obliquely downwards and to the left from the neck of the 

 gall-bladder, and joins the hepatic duct to form the common duct. It lies in 

 the gastro-hepatic omentum in front of the vena cava, the cystic artery lying 

 to its left side. The mucous membrane lining its interior is thrown into a series 

 of crescentic folds, from five to twelve in number, which project into the duct 

 in regular succession, and are directed obliquely round the tube, presenting 

 much the appearance of a continuous spiral valve. They exist only in the 

 human subject. When the duct has been distended, the interspaces between 

 the folds are dilated, so as to give to its exterior a sacculated appearance. 



The ductus communis choledochus, the largest of the three, is the common ex- 

 cretory duct of the liver and gall-bladder. It is about three inches in length, 

 of the diameter of a goose-quill, and formed by the junction of the cystic and 

 hepatic ducts. It descends along the right border of the lesser omentum, 



Fig. 412. The Parts in the Gastro-hepatic Omentum. its Anterior Layer being removed. 



behind the first portion of the duodenum, in front of the vena portae, and to 

 the right of the hepatic artery; it then passes between the pancreas and de- 

 scending portion of the duodenum, and, running for a short distance along the 

 right side of the pancreatic duct, near its termination, passes with it obliquely 

 between the mucous and muscular coats, the two opening by a common orifice 

 upon the summit of a papilla, situated at the inner side of the descending por- 

 tion of the duodenum, a little below its middle. 



Structure. The coats of the biliary ducts are, an external or fibrous, and an 

 internal or mucous. The fibrous coat is composed of a strong areolar fibrous 

 tissue. The mucous coat is continuous with the lining membrane of the hepatic 

 ducts and gall-bladder, and also with that of the duodenum. It is provided 

 with numerous glands, the orifices of which are scattered irregularly in the 

 larger ducts, but in the smaller hepatic ducts are disposed in two longitudinal 

 rows, one on each side of the vessel. These glands are of two kinds. Some 

 are ramified tubes, which occasionally anastomose, and from the sides of which 



