986 THE ORGANS OF DIGESTION 



3. The mucoKS coat is raised into ruira^ boundino: polygonal spaces, which are 

 largest about the body. It is lined with columnar epithelium, and contains many 

 mucous glands. At the neck the mucous membrane forms folds which project into 

 the interior, acting as valves. This laj'er contains an anastomosis of blood-vessels, 

 and a fine plexus of lymi)hatics. 



The duds consist of a fibrous and a mucous layer. In the filjrous layer are mus- 

 cular fibres which are chiefiy circular, together with many strong white connective 

 tissue and elastic fibres. The mucous layer is lined with columnar epithelium, and 

 has many mucous glands. In the cystic duct the mucous membrane is raised into 

 folds, which are crescentic in form, and so directed obliquely as to seem to surround 

 the lumen of the tube in a sjjiral manner. 



Varieties of the Liver 



Varieties are more rare in the liver than in almost any other organ of the body. 



The left lobe may be very small; on the other hand, it may be much larger, 

 occasionally extending in an attenuated form much more towards the left. The 

 left lobe, or a portion of it, may be attached only by a pedicle of peritoneum and 

 vessels to the main organ. The gall bladder has been seen through an opening in 

 the upper surface, owing to the depth of the fossa of the gall bladder. 



The liver may be subdivided into many lobes, or may show^ no division at all. 

 It may retain the thick rounded form of the foetus. The gall bladder may be absent, 

 in which case the hepatic duct usually Ijecomes much dilated before it reaches the 

 duodenum. 



The gall bladder may be partially divided either transversely or longitudinally. 

 The common duct may enter the bowel independently of the pancreatic duct. 



THi: PANCREAS 



The pancreas is situated in the epigastric and left hypochondriac regions. It 

 is a compound racemose gland. It lies transversely across the body, on a level Avith 

 the first and second lumbar vertebrae, and is deeply placed (fig. 577). It differs in 

 shape as it is examined in situ, or removed from the body. AA'hen examined in situ 

 it shows various impressions for the different organs with which it is in contact 

 (figs. 570, 571); when removed from the body it appears to be longer, and runs to 

 a point at tlie left extremity (fig. 587). It is of a pinkish-cream colour and soft in 

 texture. It shows upon its surface the markings between the lobules of which it is 

 made up. It may be divided into four portions: a head, a neck, a body, and a tail. 

 The pancreas varies considerably in size. Its average length is five to six inches 

 (120 to 150 mm. ), and its thickness from half an inch to one inch. It weighs from 

 2^ to 3| ounces. The head of the pancreas is situated at the right extremity of 

 the gland, and is contained in the loo}! of tlie duodenum. It is disc-shaped and 

 flattened from before })ackwards. The head is bent downwards, so that it extends 

 lower than the lower liorder of the body. Behind it are found the common bile 

 duct, which runs, as a rule, in a canal in its substance, the vena cava, the left renal 

 vein, and the aorta (fig. 571). In front are the superior mesenteric vessels, the 

 pancreatico-duodenal vessels, and the transverse colon and its meso-colon. 



The neck springs from the upper part of the head in front and turns upwards 

 and to the left to join the body. It lies over the ]ioint of junction of the superior 

 mesenteric and portal veins. At its attachment to the head it is grooved by the 

 gastro-duodenal and su]W'rior ])Hncreatico-duodenal arteries. In front of it would 

 be the first part of the duodenum. 



According to Professor Plis, tliere are three surfaces on tlic body of the pan- 

 creas : anterior, inferior, and ]tosterior. The body extends from the head of the 



