GALL BLADDER. 22Q 



in their centers the ducts are found. The actual connection between the 

 trabeculae and bile ducts is very difficult to observe in ordinary sections, 

 although it is easily seen after the ducts have been injected, or in Golgi 

 preparations (Fig. 260). The transition from hepatic cells to the low cu- 

 boidal cells of the small ducts occurs abruptly at the borders of the lobule. 

 The cuticula of the bile capillaries is continuous with that of the ducts. 

 The larger interlobular ducts have a simple columnar epithelium. They 

 are said to anastomose with one another. 



The cystic, hepatic, and common bile ducts all have a simple columnar 

 epithelium, containing occasional goblet cells. It rests on an elastic tunica 

 propria, surrounded in turn by a submucosa. In the cystic duct the mu- 

 cosa is thrown into coarse transverse folds, containing muscle fibers, known 

 as the spiral valve. In the hepatic and common bile ducts especially, 

 branched mucous glands extend into the connective tissue layer (glandnlae 

 mucosae biliosae). Outside of them is a tunica muscularis consisting 

 chiefly of circular fibers. These form a sphincter around the bile duct at 

 the duodenal papilla (and there are similar sphincters around the outlets 

 of the pancreatic ducts). The parts of the ducts exposed on the under 

 surface of the liver are covered by a serosa. 



In the gall bladder the mucosa forms a network of folds. The colum- 

 nar epithelial cells are twice the height of those in the common bile duct. 

 Goblet cells are absent and glands are infrequent. Solitary nodules may 

 be found in the mucosa. The muscular layer is of obliquely circular fibers 

 in a plexiform layer. Among them are groups of sympathetic nerve cells, 

 which innervate the muscle. There are also medullated nerve fibers in the 

 gall bladder which terminate in its epithelium. The subserous portion 

 of the serosa is highly developed and contains large lymphatic vessels. 



The vasa aberrantia of the liver are blind ducts which extend beyond 

 the territory of the trabeculae. They are found about the left lobe, and 

 especially around the vena cava, the porta hepatis and the left triangular 

 ligament, and represent portions of the liver from which the hepatic cells 

 have degenerated arid disappeared. 



The porta hepatis, meaning 'gate of the liver' is the place where the 

 vessels enter and the ducts leave, thus corresponding with the hilus of 

 other organs. There the lymphatic vessels and the nerves are very numer- 

 ous. The latter, chiefly non-medullated, form networks around the 

 vessels and ducts. They extend into the capsule and interlobular tissue, 

 chiefly supplying the blood vessels. Some, however, continue into the 

 lobules to the hepatic cells. The lymphatic vessels anastomose freely in 

 the capsule and in the interlobular tissue, these sets connecting with one 

 another. They do not enter the lobules. 



