THE BILIARY DUCTS. 21 



wall of the duct. These consist of round or elongated, often 

 caecum-like processes, having a diameter of 0'035 0'045 of a 

 millimeter, which either open directly into a biliary duct, or 

 coalesce in small numbers to form a canal, which again may 

 either open separately into the duct, or may join with others 

 to form a common excretory duct, and then resemble an 

 acinous gland. This excretory duct sometimes runs for a 

 short distance in the wall of the biliary duct, before opening 

 into it. 



The wall of the trunk and larger branches of the biliary duct 

 can be shown to consist of an internal layer of mucous mem- 

 brane and an external fibrous sheath. The latter contains 

 smooth muscular fibres (Henle) and a few bloodvessels, whilst 

 the former is lined by a single layer of tall columnar cells, and 

 supports a very close capillary plexus. The medium-sized 

 biliary ducts have a columnar epithelial layer, the cells of 

 which are not so high, and a wall composed of a single layer, 

 that, according to Heidenhain,* also contains contractile fibre- 

 cells. The finest ducts, lastly, are characterized by only pos- 

 sessing an epithelial layer, which seems to lie free in the 

 interlobular connective tissue, and consists of polyhedric cells, 

 elongated in the direction of the axis of the tube. The cuti- 

 cula, consisting of the transparent basement membrane of the 

 columnar epithelium lining the larger ducts, becoming attenu- 

 ated, is continued on the natter cells of the finer ducts, and 

 confers upon their lumen a remarkably sharp outline (Eberth). 

 The form of the nuclei of the epithelial cells accords with the 

 form of the latter ; being long-oval in the columnar cells of the 

 coarser, round in the more flattened cells of the medium-sized, 

 and oval in the cells that are somewhat elongated in the 

 direction of the axis of the tube, and which line the smallest 

 biliary ducts. 



The free surface of the mucous membrane of the common 

 hepatic duct exhibits numerous shallow, irregularly arranged 

 depressions. Similar depressions are found in the several 

 branches of the duct, down to those which do not exceed 0'5 

 of a millimeter in diameter, the only difference being that they 



* St-udien des Physiologischen Instituts zu Breslau, Heft iv., p. 241. 



