458 SPECIAL HISTOLOGY. 



All the finest glandular ducts and vesicles, whose diameter varies from 

 0-02 to 0-08 of a line, consist of a peculiar, structureless coat, the mem- 

 brana propria, of 0-0008 0*0012 of a line in thickness, and of an epi- 

 thelium (Fig. 180), which, in fresh preparations, appears as a continuous 

 investment of the glandular extremities, but is 

 Fi - 180 - very readily detached, and then fills the glan- 



dular vesicles as a granular mass. The epithelial 

 cells constitute a simple layer upon the m&mbrana 

 propria, have 36 sides, are often somewhat 

 elongated, 0-005-0-006 of a line broad, 0-003- 

 0-004 of a line thick, and invariably contain, be- 

 sides a rounded or elongated nucleus of 0-002-0-003 of a line, often 

 presenting a distinct nucleolus, a certain number of larger or smaller 

 granules, which sometimes simply resemble white fat, sometimes are 

 colored yellowish and brownish, and contribute to the hue of the glands 

 themselves. 



The elements of the glandular lobes which have been just described, 

 though they are all applied very closely together, so, indeed, as not un- 

 commonly to be flattened against one another, yet always present a 

 small quantity of interposed connective tissue, by which the vessels of 

 the lobes are supported. Besides this, the separate lobes and the entire 

 glands are invested by dense coats of a connective tissue, with elastic 

 fibres, which may, in addition, contain fat-cells. In small glands, such 

 as Fig. 178, the only distinguishable subdivisions are the lobes, glan- 

 dular vesicles, and caeca, which have been described ; in the larger, on 

 the other hand, as in the glands of the lips and palate, the smallest 

 lobes are surrounded in groups by somewhat stronger sheaths of con- 

 nective tissue, so that a certain number of secondary lobes are formed, 

 each of which corresponds with a simple gland and also has the same 

 size, i. e.j about |~1| lines. 



The excretory ducts of the* lobes have a coat of connective tissue, 

 with networks of fine elastic fibres, and a simple layer of cylindrical 

 cells 0-008-0-01 of a line thick. In -the principal excretory ducts, the 

 wall, which is very rich in elastic fibres, measures, even in the smallest 

 glands, 0-02, in the larger as much as 0-03 and 0-04 of a line, the epi- 

 thelium 0-010-012 of a line. Of muscular fibres I saw no trace what- 

 soever, either in the glands themselves or in their excretory ducts ; on 

 the other hand, they possess many minute vessels, which penetrate with 

 the excretory duct or otherwise between the lobes, and form, in the in- 

 terior, a wide network of capillaries of 0-003 of a line, which encircle 

 the separate caeca and vesicles, so that each of them is in contact with 



FIG. 180. Two glandular vesicles of a racemose mucous gland of Man, magnified 300 

 diameters; a, membrana propria ; 6, epithelium, as it appears in the apparent section of a 

 vesicle; c, the same seen upon its surface. 



