THE EXCRETORY DUCTS. 



connection with the regeneration of the gland tissue. Lastly, 

 from these tubes, lined by tall columnar cells, richly fibrillated 

 at their base, and which appear to be present in all similarly 

 constructed acinous glands, fine canals are given off' either by 

 gradual or sudden transition of the epithelium. The canals 

 are not much thicker than capillaries, and present characters 

 which, both in regard to their size and in the dimensions of the 

 cells composing the simple epithelial tubes, are similar to those 

 of all the allied acinous glands. These cells are always much 

 flattened, and are usually characterized by the presence of very 

 substantial processes, which give them a fusiform appearance, or 

 some form analogous to a spindle. They lie with their long axis 

 parallel to the axis of the epithelial tube, and are frequently 

 arranged in an imbricated manner. The canals are finally 

 connected with the alveoli by means of short branches, which, 

 being formed for the most part of from four to six epithelial 

 cells, are prolonged into the interior of the alveoli, where 

 they are invested almost circularly by the peculiar secreting 

 epithelial cells. These last, and still more the former, cells of 

 the excretory ducts, occupying almost the centre of the alveolus, 

 penetrate by means of their processes between the secreting 

 epithelial cells, and have been named by Langerhans (in the 

 pancreas) ' centro-acinar ' cells. 



Whilst formerly a very simple form was attributed to the 

 cavity situated in the interior of the alveolus, into which the 

 secreting epithelial cells poured their secretion, investigations 

 undertaken with improved methods of injection by Giannuzzi, 

 Langerhans, Ewald, and Saviotti, have shown that the simple 

 short and minute excretory duct of the alveolus breaks up into 

 a very rich, much branched, and frequently anastomosing plexus 

 of extremely fine cylindrical canals, which, in exactly the same 

 mode as that given by Hering of the relations of the finest 

 biliary ducts to to the hepatic cells, invests the individual 

 epithelial cells, and includes them in its meshes. The canals lose 

 their proper membrane, and beyond this point merely form 

 sparingly distributed ducts situated between the variously 

 formed polyhedric gland cells, which are in close apposition 

 with each other, and are provided both along their borders 

 and surfaces with grooves. 



