438 



EXCRETION. 



the union of two ducts, one from the right and the other from the left lobe of the liver. 

 It is about an inch and a half in length and joins at an acute angle with the cystic duct, 

 to form the ductus communis choledochus. The common duct is about three inches in 

 length, of the diameter of a goose-quill, and it opens into the descending portion of the 

 duodenum. It passes obliquely through the coats of the intestine and opens into its 

 cavity, in connection with the principal pancreatic duct. The cystic duct is about an 

 inch in length and is the smallest of the three canals. 



20 12 10 



FIG. 134. Gall-bladder, hepatic, cystic, and common ducts. (Sappey.) 



1, 2, 3, duodenum ; 4, 4, 5, 6, 7, 7, 8, pancreas and pancreatic ducts ; 9, 10, 11, 12, 13, liver ; 14, gall-bladder; 15, hepatic 

 duct; 16, cystic duct; 17, common duct; 18, portal vein; 19, branch from the coeliac axis ; 20, hepatic artery; 21, 

 coronary artery of the stomach ; 22, cardiac portion of the stomach ; 23, splenic artery ; 24, spleen; 25, left kidney ; 

 26, right kidney ; 27, superior mesenteric artery and vein ; 28, inferior vena cava. 



The structure of these ducts is essentially the same. They have a proper coat, formed 

 of white fibrous tissue, a few elastic fibres, and a few non-striated muscular fibres. The 

 muscular tissue is not sufficiently distinct to form a separate coat. The mucous mem- 

 brane is always found tinged yellow with the bile, even in living animals. It is marked 

 by numerous minute excavations and is covered with cells of columnar epithelium. This 

 membrane contains numerous mucous glands. 



The gall-bladder is an ovoid or pear-shaped sac, about four inches in length, one inch 

 in breadth at its widest portion, and capable of holding from an ounce to an ounce and a 

 half of fluid. Its fundus is covered entirely with peritoneum, but this membrane passes 

 only over the lower surface of its body. 



The proper coat of the gall-bladder is composed of white fibrous tissue with a few 

 elastic fibres. In some of the lower animals there is a distinct muscular coat, but a few 

 1 scattered fibres only are found in the human subject. The mucous coat is of a yellowish 

 color and marked with numerous very small, interlacing folds, which are exceedingly 

 vascular. Like the membrane of the ducts, the mucous lining of the gall-bladder is cov- 

 ered with columnar epithelium. In the gall-bladder, are found numerous small racemose 

 glands, formed of from four to eight follicles lodged in the submucous structure. These 

 are essentially the same as the glands opening into the ducts in the substance of the liver, 

 and they secrete a mucus which is mixed with the bile. 



