682 ORGANS OF DIGESTION. 



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 excre- 

 tory 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, 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 descending 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 portion of the duodenum, a 

 little below its middle. 



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

 and an internal or mucous layer. 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 saccular dila- 

 tations are given off; others are small clustered cellular glands, which open either 

 separately into the hepatic duct, or into the ducts of the tubular glands. 



THE PANCREAS. 



Dissection. The pancreas may be exposed for dissection in three different ways : 1. By raising 

 the liver, drawing down the stomach, and tearing through the gastro-hepatic omentum. 2. By 

 raising the stomach, the arch of the colon, and great omentum upwards, and then dividing the 

 inferior layer of the transverse mesocolon. 3. By dividing the two layers of peritoneum, which 

 descend from the great curvature of the stomach to form the great omentum ; turning this organ 

 upwards, and then cutting through the ascending layer of the transverse mesocolon. 



The Pancreas (itav-xpia^ all flesli) is a conglomerate gland, analogous in its 

 structure to the salivary glands. In shape, it is transversely oblong, flattened 

 from before backwards, and bears some slight resemblance to a hammer, its right 

 extremity being broad, and presenting a sort of angular bend from above down- 

 wards, called the head; its left extremity gradually tapers to form the tail, the 

 intermediate portion being called the lody. It is situated transversely across the 

 posterior wall of the abdomen, at the back of the epigastric and both hypochon- 

 driac regions. Its length varies from six to eight inches, its breadth is an inch 

 and a half, and its thickness from half an inch to an inch, being thicker at its 

 right extremity and along its upper border. Its weight varies from two to three 

 and a half ounces, but it may reach six ounces. 



The right extremity or head of the pancreas (fig. 346) is curved upon itself 

 from above downwards, and is embraced by the concavity of the duodenum. The 

 common bile duct descends behind, between the duodenum and pancreas ; and the 

 pancreatico-duodenal artery descends in front between the same parts. Upon its 

 posterior part is a lobular fold of the gland, which passes transversely to the left, 

 behind the superior mesenteric vessels, forming the back part of the canal, in 



