The walls of the gall-bladder are about 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 is 0.4 to 0.5 mm. thick, and 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 surface 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 connective 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 are found scattered here and there in the walls of the gall-bladder. Sections from this organ, hardened 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.
