100 



GENERAL ANATOMY OF THE TISSUES. 



3. Rounded or elongated glandular vesicles, with a membrana 

 propria and an epithelium. In the racemose glands (fig. 41). 



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

 membrane and an epithelium. Tubular glauds (fig. 42). 



Fig. 41. 



Fig. 40. 



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 tubu- 

 lar glands) special excretory ducts, which, after manifold rami- 

 fications, 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 ako 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 structures. 



Chemically, the glands are, as yet, little known. The glan- 

 dular cells, as the most important structures, are allied in this 

 respect also, to the epithelial structures, only that frequently, 



Fig. 40. Network of hepatic cells, b; and finest ductus interlobulares, a; of man 

 after nature; the union of both diagrammatic, x 350 ; c, vascular spaces. 



Fig. 41. Two of the smallest lobes of the lung, aa ; with air-cells, lib; and the 

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

 born child, x 25 ; semi- diagrammatic figure. 



