1198 



SPLANCHNOLOGY 





of the descending portion of the duodenum, but sometimes with the superior portion of the 

 duodenum or pyloric end of the stomach. The fundus is completely invested by peritoneum; 

 it is in relation, in front, with the abdominal parietes, immediately below the ninth costal car- 

 tilage; behind with the transverse colon. The neck is narrow, and curves upon itself like the 

 letter S; at its point of connection with the cystic duct it presents a well-marked constriction. 



Columnar epithelium 



Fibro-muscular 

 coat 



Liver-cells 



FIG. 1096. Transverse section of gall-bladder. 



Structure ( Fig. 1036). The gall-bladder consists of three coats: serous, fibromuscular, and 

 mucous. 



The external or serous coat (tunica serosa vesicae felleae) is derived from the peritoneum; it 

 completely invests the fundus, but covers the body and neck only on their under surfaces. 



The fibromuscular coat (tunica muscularis vesicce fellece), a thin but strong layer forming the 

 frame-work of the sac, consists of dense fibrous tissue, which interlaces in all directions, and is 

 mixed with plain muscular fibers, disposed chiefly in a longitudinal direction, a few running 

 transversely. 



The internal or mucous coat (tunica mucosa vesicce felleve) is loosely connected with the fibrous 

 layer. It is generally of a yellowish-brown color, and is elevated into minute rugae. Opposite 

 the neck of the gall-bladder the mucous membrane projects inward in the form of oblique ridges 

 or folds, forming a sort of spiral valve. 



The mucous membrane is continuous through the hepatic duct with the mucous membrane 

 lining the ducts of the liver, and through the common bile duct with the mucous membrane of 

 the duodenum. It is covered with columnar epithelium, and secretes mucin; in some animals 

 it secretes a nucleoprotein instead of mucin. 



The Cystic Duct (ductus cysticus). The cystic duct about 4 cm. long, runs back- 

 ward, downward, and to the left from the neck of the gall-bladder, and joins the 

 hepatic duct to form the common bile duct. The mucous membrane lining its 

 interior is thrown into a series of crescentic folds, from five to twelve in number, 

 similar to those found in the neck of the gall-bladder. They project into the duct 

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

 much the appearance of a continuous spiral valve. When the duct is distended, 

 the spaces between the folds are dilated, so as to give to its exterior a twisted 

 appearance. 



The Common Bile Duct (ductus choledochus) . The common bile duct is formed 

 by the junction of the cystic and hepatic ducts; it is about 7.5 cm. long, and of the 

 diameter of a goose-quill. 



It descends along the right border of the lesser omentum behind the superior 

 portion of the duodenum, in front of the portal vein, and to the right of the hepatic 

 artery; it then runs in a groove near the right border of the posterior surface of the 

 head of the pancreas; here it is situated in front of the inferior vena cava, and is 

 occasionally completely imbedded in the pancreatic substance. At its termination 

 it lies for a short distance along the right side of the terminal part of the pancreatic 

 duct and passes with it obliquely between the mucous and muscular coats. The 



