182 



NORMAL HISTOLOGY. 



and beset with scattered small tubular glands. These, as well as the 

 surface epithelium, contain many goblet-cells producing a mucous secretion. 

 Bundles of unstriped muscle occur within the deeper parts of the tunica 

 propria; they are neither numerous nor regularly disposed in definite layers, 

 the chief longitudinal ones being supplemented by circular and oblique bun- 

 dles. As the duct-system is, followed into the capsule of Glisson, the muscle 

 disappears from the walls of all but the larger interlobular bile-vessels, while 

 the fibro-elastic coat also gradually diminishes. Apart from the reduction 

 in height of the cells, the lining of the ducts retains throughout its character 

 of simple columnar epithelium, thus affording a ready means of distinguishing 

 the, bile-ducts from the blood-vessels as they course together between the 

 lobules. The existence of former masses of hepatic tissue, which have dis- 

 appeared during development and growth, is indicated by the blind ducts, 

 known as the vasa aberrantia, found outside the liver-substance along the 

 left border of the liver, around the inferior vena cava and in the vicinity of 

 the transverse fissure. 



The gall-bladder, the pear-shaped receptacle for the bile attached to 

 the under side of the liver near its anterior border, possesses strong walls 

 consisting of three coats: the mucous, the muscular and the fibrous, the 



Epithelium 



Blood-vessel 



Muscle 



FIG. 227. Section of wall of gall-bladder, showing plicated condition of mucous membrane. X 100. 



latter supplemented by a more or less extensive investment of peritoneum. 

 The mucous coat, covered with a single layer of columnar epithelium about 

 5 fj. thick, is modelled by a network of slightly raised ridges that mark off 

 irregular polygonal areas some 5 mm. in diameter. These areas are often 

 marked by minute tubular depressions of the mucosa which have been mis- 

 taken for glands. True branched mucous glands occur in the neck of the 

 gall-bladder, but are so few in other parts of the sac as to be practically 

 wanting. The epithelial cells exhibit a cuticular border and are often of 

 the goblet type and concerned in producing a mucous secretion. The 

 tunica propria contains a profusion of elastic fibres intermingled with the 

 white fibrous tissue. The muscular coat is composed for the most part of 

 circular bundles of unstriped fibres, but with these are interwoven longitudinal 



