COLUMNAR EPITHELIUM. Ivii 



throughout, but are more frequently smaller or even pointed at their 

 lower or attached extremity, and broader at the upper (fig. xxv. A). 

 They are mostly flattened on their sides, by which they are in mutual 

 apposition, at least in their upper and broader part, and have, therefore, 

 so far a prismatic figure, their broad flat ends appearing at the surface of 

 the epithelium in form of little polygonal areas (fig. xxv. B.) The nucleus, 

 usually oval, and containing a nucleolus, is placed near the middle of the 

 column, and is often so large in proportion to the cell, as to cause a bulging 

 at that part ; in which case the height of the nucleus differs in contiguous 

 columns, the better to allow of mutual adaptation. 



This variety of epithelium is 



confined to mucous membranes. Fi gt XXVI. 



It is found in the stomach ; on 

 the mucous membrane of the 

 intestines in its whole extent ; 

 in the whole length of the 

 urethra, except a small part at 

 the orifice. It extends along 

 the ducts of the greater number 

 of glands, whether large or 

 small, which open on the mu- Fig. XXVI. EPITHELIUM PROM INTESTINAL 

 cous membrane, but not through VILLUS OP A RABBIT; MAGNIFIED 300 DIA- 

 their entire length ; for, at their 



extremities, these ducts have for , Thick border (from Kolliker). 

 the most part an epithelium of 

 a different character. It covers also the inner membrane of the gall-bladder. 



In these different situations the cells form but a single layer. On the 

 proper olfactory region of the nasal mucous membrane there is a modification 

 of the columnar epithelium, in which the cells, tinged with brownish yellow 

 pigment, are associated with the terminations of the olfactory nerves, and 

 present other peculiarities, which will be noticed in the special description of 

 the organ of smelling. 



The substance ordinarily contained in the columnar cells has a faintly granular 

 aspect, and consists chiefly of mucus, which is no doubt produced in the cell. Under 

 exposure to water this mucus swells up and escapes in form of a pellucid drop 

 (fig. xxvu., a, 6). During digestion of food containing oil or fat, the cells of the 

 intestinal epithelium are often found to be filled with minute fat-molecules ; as if 

 they had some part to perform in the absorption of that aliment. The wall of the 

 cell forming the basis or free end is comparatively thick (fig. xxvi., a), and is marked 

 by fine parallel lines running perpendicular to the surface (fig. xxvu., 1, 2). The 

 thick, striated border is superadded, as it were, to the thin proper wall forming the 

 base of the cell, and is regarded by Kolliker, who first pointed out its striated 

 character, as an excreted product of the cell, deposited upon its outer surface, as 

 occurs in the cuticular structures of many of the inferior animals. As to the striation, 

 it might no doubt be produced by a fine columnar or fibrous structure, but most 

 observers agree with Kolliker in ascribing it to fine tubular passages perforating the 

 cell-wall ; and it is further supposed that such porous structure would account for the 

 assumption of fat-molecules or other minutely divided matters into the cell, and may 

 be subservient to an absorptive function in cells so constituted. It must be stated, 

 however, that a thickened striated border has been since observed in various other 

 epithelium cells which are not so obviously connected with the function of absorption, 

 such as those lining the biliary and urinary passages, and the parotid and pancreatic 

 ducts. 



As fat, in a state of minute division, is undoubtedly taken into the epithelium-cells 

 of the intestinal villi, and disappears from them again, it was natural to look for some 



