TISSUES, ORGANS, AND SYSTEMS. 



113 



1846, Nos. G87-699, and 1848, No. 733 ; Kcilliker, " Neurologische 

 Bemcrkungcn," in " Zcitsch. fur Aviss. Zool.," i. p. 185. 



§29. True Glandular Tissue. — The most essential constituents of the 

 true glands arc the secreting elements., which appear as aggregations of 

 cells, as closed glandular vesicles, and as open glandular vesicles and 

 glandular tubes, containing as their most important constituent the so- 

 called gland-cells. These cells are for the most part polygonal or cylin- 

 drical, and perfectly resemble certain epithelial cells, but upon the other 

 hand, they are frequently distinguished and characterized by peculiar 

 contents. The union of these cells into the secreting parts of the glands 

 is efiected either directly or with the co-operation of homogeneous mem- 

 branes, the so-called memhrance propria;, and of connective tissue. In 

 this manner the secreting glandular elements, different in nature accord- 

 ing to the different glands, are formed ; and becoming invested with 

 vessels, nerves, and connective tissue, with which elastic fibres, fat- 

 cells, and even muscles, are mingled, they are combined into the larger 

 and smaller divisions of the glands. The principal forms of the secret- 

 ing glandular elements in man are the following : — 



1. Solid networks of cells without investing membrane. In the liver 

 (Fig. 40). 



2, Closed vesicles with a fibrous membrane and epithelium. Graafian 

 vesicles, mucous follicles (so-called ovula Nabotld), in the cervix uteri. 



FiR. 40. 



Fix. 41. 



3. Rounded or elongated glandular vesicles, ivith a meynbrana propria 

 and an epithelium. In the racemose glands (Fig. 41). 



Fig. 40. — Network of hepatic cells, b ; and finest ductus inlerlobulares, a ; of man after 

 nature; the union of both diagrammatic; c, vascular spaces. — Magnified 350 diameters. 



Fig. 41. — Two of the smallest lobes of the lung, a a ; with air-cells, b b ; and the finest 

 bronchial ramifications, cc; upon which also air-cells are seated. From a new-born chiUl ; 

 semi-diagrammatic figure. — Magnified 25 diameters. 



S 



