114 



GENERAL ANATOMY OF THE TISSUES. 



Fig. 42. 



4. Glandular tubes, with a membrana propria, or a fibrous membrane 

 and an epithelium. Tubular glands (Fig. 42). 



To these elements are also added (except in those glands enumerated 

 under 2, which become emptied of their contents by the occasional 

 bursting of their follicles, and the simplest tubular glands) special excre- 

 tory ducts, which, after manifold ramifications either pass directly into 

 the glandular vesicles and glandular tubes, or, as in the liver, are simply 

 applied to the secreting networks of cells. These ducts are at first 

 similar in their structure to the secreting parts, but they always possess 

 epithelial cells, which have not the specific contents of the proper gland 

 cells, and mostly also exhibit a different form. The wider excretory 

 ducts consist of a fibrous investment and of an epithelium, and often 

 also, possess a muscular layer, and in their ultimate divisions, a fibrous, 

 a muscular, and a mucous layer very frequently exist as special struc- 

 tures. 



Chemically, the glands are, as yet, little known. The glandular 

 cells, the most important structures, are allied in this respect also to the 

 epithelial structures, only that frequently, they contain in their interior 

 peculiar substances, as fat, the constituents of the bile, of the urine, of 

 the gastric juice, mucus, &c., and thence assume a specific character. 



The true glands either separate certain constituents 

 from the blood, or by means of it, elaborate peculiar 

 substances of structural elements, and according as 

 they do the one or the other, is the import of their 

 separate parts different. In the former glands the 

 cells play a more subordinate part, and are at most 

 of importance, so far merely, as they impede the 

 passage of this or that constituent of the blood, and 

 allow only certain of them to pass (kidneys, lachrymal 

 glands, small sudoriparous glands, lungs) ; whilst in 

 others, the cells take a very important share in the 

 formation of the glandular fluid, by producing within 

 them the specific secretion, which then either drains 

 out of them (liver, mucous glands, gastric glands, pro- 

 state, Cowper's glands, salivary glands, pancreas), or be- 

 comes free by the gradual dissolution and breaking up of 

 the cells themselves (lacteal glands, fat glands, testis, 

 larger sudoriparous and ceruminous glands). In the for- 

 mer case, as in the Graafian follicles, a peculiar cell- 

 development may take place in the secretion which is 

 formed, whilst in the latter, new elements continually arise in place of 

 those gland-cells which are removed as they attain their full develop- 



FiG. 42. Gastric gland from the pylorus of the dog, with cylinder-epithelium : a, larger 

 glandular cavity ; 6, tubular appendages of it. 



