708 THE BILE-DUCTS. [BOOK n. 



into the vascular meshwork of the marginal parts of the lobules, 

 but this is disputed. 



448. The Bile-ducts. The larger bile-ducts, namely, the 

 hepatic duct leading from the liver, the cystic duct leading from 

 the gall-bladder, and the common bile-duct formed by the junction 

 of the two, have the ordinary characters of large gland-ducts. An 

 epithelium of columnar cells rests on a connective tissue basis, and 

 so constitutes a mucous membrane ; this is supported by a well- 

 developed muscular coat, consisting of a thicker internal layer of 

 circularly disposed, and a thinner external layer of longitudinally 

 disposed, plain muscular fibres mixed up with a good deal of con- 

 nective tissue. The walls of the gall-bladder have essentially the 

 same structure. Both the gall-bladder and the ducts are capable 

 of carrying out peristaltic contractions of their walls, by the help 

 of which when needed ( 252*) the rapid flow of bile into the 

 intestine is secured. 



The bile-ducts within the liver are also similarly constituted, 

 their walls of course becoming thinner and less muscular as the 

 tubes diminish in size, and the epithelium becoming cubical rather 

 than columnar. A characteristic feature of the smaller bile-ducts 

 as they run in Glisson's capsule is that, unlike the ducts of most 

 glands, they form frequent anastomoses. 



The epithelium of the ducts contains many goblet cells, and 

 in the walls of the larger ducts and of the gall-bladder small 

 mucous glands are present ; in the smaller ducts these are apt to 

 be simplified into mere pits or short depressions of the mucous 

 membrane. 



The small terminal anastomosing bile-ducts, now consisting of 

 hardly more than a cubical epithelium resting on a connective 

 tissue basis, may be traced to various points of the margin of a 

 lobule and there seem to end abruptly. Just before a bile-duct 

 thus ends or seems to end, the cubical cells become much flatter, 

 the lumen of the tube however remaining narrow ; and then the 

 end of the tube seems blocked up with the hepatic cells of the 

 lobule. To understand, however, the nature of this peculiar ending 

 we must return to the hepatic cells. 



449. The hepatic cells filling up the meshes of the vascular 

 network of a lobule are relatively large (20 to 30 /x in diameter in 

 man) polygonal or roughly cubical cells. Each contains a relatively 

 large rounded nucleus, and in not a few cells two nuclei may be 

 seen. Each cell is partly in contact with its neighbours, and 

 partly abuts on a blood vessel ; for there is probably not a cell in 

 a lobule which is not in touch, for some part of its surface, with 

 one or more blood vessels. Where the surfaces of two cells meet 

 their substances are in contact, that is to say, there is no cement 

 substance between them, and the external layer of cell-substance, 

 though it may at times at all events differ from the more internal 

 cell-substanceJ^is not differentiated into a distinct membrane or 



