328 PKOFESS01{ FRANK J. COLE 



outlines are not very clearly defined, and the free border is somewhat modified and 

 tends to flake off" into the lumen of the duct. Occasionally an isolated nucleus in 

 mitosis may be seen between the row of basal nuclei and the free border. 



The wall of the gall bladder is not perforated by the hepatic ducts at right angles 

 to its surface, but very obliquely, with the result that a flap is formed which acts as a 

 valve to the opening. At this point the transition from the epithelium of the hepatic 

 duct to that of the gall bladder may be well studied. The cells of the duct become 

 shallower and vacuolated, the non- staining areas between the cells appear, the 

 modification of the free border becomes emphasised into the moniliform strip of the 

 gall bladder epithelium, and the clear vesicular nuclei pass into the solid irregular nuclei 

 of the bladder. On the side of the valve the transition from one kind of nucleus to 

 the other is more sudden. 



6. Histology of the Bile Duct. 



The bile duct, like the hepatic ducts, consists of a single layer of irregular epithelium 

 exhibiting numerous mitoses and without a basement membrane, and surrounded by 

 connective-tissue coats. There are, however, some obvious differences. It is, of course, 

 larger, and has a diameter of 525 m in a moderate-sized specimen outside the region of 

 the "pancreas." The lumen accounts for at most 225 m of this. The wall is also 

 somewhat thicker than that of the hepatic duct, but, owing to the pitting of the 

 epithelial lining, this varies very greatly. In an average case the epithelium is 105 /« 

 tall, and the connective-tissue coat 75 /«. The bile duct perforates the gall bladder 

 more or less obliquely, but the aperture appears to be permanently and widely open, 

 since I find no signs either of a sphincter or a valve. The transition of the epithelium 

 of the bile duct into that of the gall bladder resembles that elsewhere described in the 

 case of the hcDatic ducts. 



J. 



As the bile duct approaches the gut its wall becomes thickened owing to the 

 presence of the "pancreas," the acini of which are situated within the thickness of the 

 connective-tissue sheath of the bile duct. The latter penetrates the wall of the gut 

 almost at right angles, and has a large opening at the apex of a prominent papilla, the 

 connective-tissue coats being here of greater thickness. At the base of this papilla 

 the lumen narrows down somewhat, but so far I have not found more than a sparse 

 collection of unstriped muscle fibre in connection with the opening into the gut, and in 

 fact there may be only equivocal traces of unstriped muscle in any part of the bile duct. 

 In other examples, however, an unstriped layer immediately external to the epithelium 

 is plainly establishable. 



The lumen of the bile duct is not regular, but is thrown into many pits or bags. 

 This is due both to the folding of the epithelium, and also, and rather, to the variability 

 in height of the cells themselves. Many of the pits are long and narrow, as if they 

 were the terminations of glandular ducts ; but in nearly all cases they end blindly, in 

 a few cases in an ampulliform enlargement, without reaching the periphery of the 



