198 MANUAL OF HISTOLOGY. 



2 mm. thick, and are composed of three coats : ' an internal, 

 mucous and muscular ; a middle, of connective tissue ; and 

 an external, the serous. The internal coat, 0.4 to 0.5 mm. 

 thick, is composed of alternating layers of connective tissue 

 and smooth muscle fibres, the most internal being a layer of 

 connective tissue which contains a fine meshed capillary net- 

 work. The connective tissue is dense and the muscle fibres are 

 arranged in the form of interlacing bands. The internal sur- 

 face is lined by a layer of cylindrical cells bearing a thickened, 

 striated edge, and the surface is traversed by a network of 

 small intersecting ridges, forming, as it were, a sort of lattice- 

 work. The middle coat, 0.5 to 1 mm. thick, is formed of con- 

 nective tissue, the meshes of which are wider on the internal 

 than at the external surface. This coat contains the larger 

 vessels and nerves. The external, or serous coat is thin, and 

 consists of a layer of dense connective tissue and peritoneum. 

 A few mucous glands 2 are found scattered here and there in 

 the walls of the gall-bladder. Sections from this organ, hard- 

 ened in alcohol, may be stained with the carmine or picro-car- 

 mine solution and mounted in glycerine or balsam. 



The cystic and common ducts resemble in structure the 

 hepatic duct. The inner surface of the former is thrown into 

 crescentic ridges, and in the region of the neck of the gall- 

 bladder the connective tissue of the internal coat shows a 

 circular arrangement. The ducts contain no muscle fibres. 



The lymph-vessels. These may be divided into a series 

 of superficial and deep channels. The former are situated in 

 the capsule of the .liver and form a capillary reticulum with 

 small meshes, the larger branches of which accompany the 

 arteries in pairs and communicate with each other by trans- 

 verse anastomoses. They are found in Glisson's capsule, and 

 they also form a network somewhat larger meshed than the 

 preceding. They accompany the hepatic artery and portal 

 vein and their branches into the interior of the liver, and form 

 anastomoses with the superficial lymph- vessels. The lymph- 

 canals may easily be injected with colored material (carmine- 

 glycerine) by filling a large hypodermic syringe with the liquid 

 and injecting one of the larger lymph-vessels in the hilus of 



1 Henle : Eingeweidelehre. 



2 Luschka: Virchow's Archiv, 1857, and Zeitschr. f. rat. Med., 1858. 



