942 THE ORGANS OF DIGESTION. 



laries : (2) the gall-bladder, which serves as a reservoir for the bile ; (3) the cystic 

 duct, which is the duct of the gall-bladder ; and (4) the common bile-duct, formed 

 by the junction of the hepatic and cystic ducts. 



The Hepatic Duct. Two main trunks of nearly equal size issue from the liver 

 at the transverse fissure, one from the right, the other from the left lobe ; these 

 unite to form the hepatic duct, which then passes downward and to the right for 

 about an inch and a half, between the layers of the lesser omentum, where it is 

 joined at an acute angle by the cystic duct, and so forms the ductus communis 

 choledochus. The hepatic duct, as it descends from the transverse fissure of the 

 liver, between the two layers of the lesser omentum, lies in company with the 

 hepatic artery and portal vein. 



The Gall-bladder is the reservoir for the bile ; it is a conical or pear-shaped 

 musculo-membranous sac, lodged in a fossa on the under surface of the right lobe 

 of the liver, and extending from near the right extremity of the transverse fissure 

 to the anterior border of the organ. It is about four inches in length, one inch in 

 breadth at its widest part, and holds from eight to ten drachms. It is divided into 

 a fundus, body, and neck. The fundus, or broad extremity, is directed downward, 

 forward, and to the right, and projects beyond the anterior border of the liver ; 

 the body and neck are directed upward and backward to the left. The upper sur- 

 face of the gall-bladder is attached to the liver by connective tissue and vessels. 

 The under surface is covered by peritoneum, which is reflected on to it from the 

 surface of the liver. Occasionally the whole of the organ is invested by the serous 

 membrane, and is then connected to the liver by a kind of mesentery. 



Eolations. The body of the gall-bladder is in relation, by its upper surface, 

 with the liver, to which it is connected by areolar tissue and vessels ; by its under 

 surface, with the commencement of the transverse colon ; and further back, with 

 the upper end of the descending portion of the duodenum or sometimes with the 

 pyloric end of the stomach or first portion of the duodenum. The fundus is com- 

 pletely invested by peritoneum ; it is in relation, in front, with the abdominal 

 parietes, immediately below the ninth costal cartilage ; behind with the transverse 

 arch of the 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. 



When the gall-bladder is distended with bile or calculi, the fundus may be felt through the 

 abdominal parietes, especially in an emaciated subject : the relations of this sac will also serve to 

 explain the occasional occurrence of abdominal biliary fistulae, through which biliary calculi may 

 pass out, and of the passage of calculi from the gall-bladder into the stomach, duodenum, or 

 colon, which occasionally happens. 



Structure. The gall-bladder consists of three coats serous, fibrous and mus- 

 cular, and mucous. 



The external or serous coat is derived from the peritoneum ; it completely in- 

 vests the fundus, but covers the body and neck only on their under surface. 



The fibro-muscular coat is a thin but strong layer which forms the framework 

 of the sac, consisting of dense fibrous tissue which interlaces in all directions and 

 is mixed with plain muscular fibres which are disposed chiefly in a longitudinal 

 direction, a few running transversely. 



The internal or mucous coat is loosely connected with the fibrous layer. It is 

 generally tinged with a yellowish-brown color, and is everywhere elevated into 

 minute rugse, by the union of which numerous meshes are formed ; the depressed 

 intervening spaces having a polygonal outline. The meshes are smaller at the 

 fundus and neck, being most developed about the centre of the sac. Opposite the 

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

 oblique ridges or folds, forming a sort of screw-like valve. 



The mucous membrane is covered with columnar epithelium, and secretes an 

 abundance of thick viscid mucus ; it is continuous through the hepatic duct with 

 the mucous membrane lining the ducts of the liver, and through the ductus com- 

 munis choledochus with the mucous membrane of the alimentary canal. 



