464 



the numerous branches of the minute ducts have not been injected ; 

 and from observations upon these specimens alone, he feels that only 

 a very imperfect idea can be formed of their number or of their 

 arrangement. 



Diameter of the ducts. A table is given, showing the thickness 

 of the coats of the ducts in different parts of their course. The 

 walls of the smallest ducts are composed entirely of basement mem- 

 brane, and are often not more than the 5 Q O th of an inch in diame- 

 ter in the uninjected state. In the pig, the diameter of the smallest 

 ducts containing injection was about the 3 J Q O th of an inch ; in the 

 human subject, about the g^^th ; in the seal, 3 ^ O th ; and in some 

 fishes not more than the 5 J O th of an inch. It may be remarked, 

 that this narrowing of the excretory duct, just before it becomes 

 continuous with the secreting portion of the organ, is seen in the 

 kidney and in other glands. 



Epithelium of the small ducts. The epithelium lining the small- 

 est ducts presents very similar characters in different animals. The 

 small cells are for the most part oval or circular in form ; sometimes 

 they are angular, which probably results from pressure or stretch- 

 ing of the ducts in the preparation of the specimen ; sometimes the 

 smallest ducts appear to be entirely filled with epithelium ; in other 

 instances the cells are very sparingly and irregularly scattered over 

 the interior of the tube, while frequently no cells whatever cau be 

 distinguished. 



The author believes that, in a perfectly normal state, the minute 

 ducts are lined by a single layer of delicate epithelial cells. 



This ductal epithelium does not pass gradually into the secreting 

 epithelium, but ceases at the point where the latter begins. Hepa- 

 tic cells are sometimes seen in tubes lined with this ductal epithe- 

 lium, but probably their presence is the result of accident. In these 

 cases the ducts are of course much stretched or dilated *. 



With reference to the relation of the ductal epithelium to the 

 secreting cells of the liver, the author observes that a very similar 

 arrangement occurs in the gastric glands. The secreting epithe- 

 lium is alone found in the lower part of the gland (stomach tube), 

 while the ductal portion of the gland is lined with columnar epi- 

 thelium. 

 * Mr. Wharton Jones has also seen hepatic cells in the small ducts. Phil. Trans. 



