THE LIVER 



1189 



In its oblique course through the duodenal wall, the common bile duct is accompanied by 

 the pancreatic duct, the two together usually causing the pUca longitudinaUs duodeni (fig. 922). 

 Circular muscle fibres join with bundles of longitudinal fibres at the lower part of the ducts 

 and form a sphincter around each (fig. 950). Contraction of the sphincter probably closes the 

 orifice ofjthe common bile duct, so that (except during digestion) the bile is backed up into the 

 gall-bladder. 



Structure of the gall-bladder. — The wall of the gall-bladder is made up of three coats— 

 mucosa, fibro-muscular and serosa. 



Fig. 950. — Macerated Duodenal Portion of the Common Bile Duct, SnowaNG 

 Musculature. £, Common bile duct. IF, Pancreatic duct (of Wirsung). (S, 7^, Sphincter 

 fibres of bile duct. //, Fibres of pancreatic duct. (Hendrickson.) 



W 



1. The mucosa is raised into folds bounding polygonal spaces, giving the interior a honey- 

 comb appearance. It is lined with columnar epithelium, and contains a few tubular mucous 

 glands and lymph-nodules, and is limited externally by a poorly developed muscularis mucosae. 

 At the neck the mucous membrane forms valve-like folds which project into the interior. This 

 layer contains an anastomosis of blood-vessels, the capillaries being most numerous in the folds 

 of the mucosa, and a fine plexus of lymphatics. 



2. The fibro-muscular coat consists of interlacing bundles of non-striated muscle and fibrous 

 tissue not definitely arranged, the muscular bundles running longitudinally and obliquely- 

 This layer contains the principal blood-vessels and lymphatics, and also a nerve plexus. 



Fig. 951. — Diagrams of the Development of the Liver. (Lewis and Stohr.) 

 A, The condition in a 4.0 mm. human embryo. B, A 12 mm. pig. C, The arrangement of 

 ducts in the human adult, c. d., Cystic duct; c. p., cavity of the peritoneum; d., duodenum; 

 d.c, ductus choledochus; dia., diaphragm; div., diverticulum; /. I., falciform ligament; g. b., 

 gall bladder; g. o., greater omentum; h. d., hepatic duct; ht., heart; int., intestine; li., liver; 

 I.O., lesser omentum; m., mediastinum; oe., oesophagus; p. c, pericardial cavity; p. d. pan- 

 creatic duct; ph., pharynx; p. v., portal vein; st , stomach; tr., trabecula; v. c. i., vena cava in- 

 ferior; v.v. vitelline vein; y. s., yolk sac. 



3. The serosa being formed by the peritoneum, is only found on the lower surface and part 

 of the sides. 



The ducts consist of a fibro-muscular and a mucous layer. In the fibro-muscular layer are 

 non-striated muscle-cells which are chiefly circular, together with white fibrous tissue and elastic 

 fibres. The mucous layer is lined with columnar epithehum, and has many mucous glands. In 

 the cystic duct the mucous membrane is raised into folds, which are crescentic in form, and 

 directed so obUquely as to seem to surround the lumen of the tube in a spiral manner. 



The development of the liver. — The relations which the hver bears to the diaphragm, to 

 its vessels and more especially the veins, and to its so-caUed hgaments, may be understood by 

 a reference to its development (figs. 951, 952). In discussing the development of the peritoneum 

 and the mesenteries it was shown that the liver has its origin in a bud of entoderm, which grows 



