SECEETIXG GLANDS. 401 



the former is not peculiar, and need not be here con- 

 sidered. Nerve-fibres are distributed both to the blood- 

 vessels of the gland and to its ducts ; and, in some glands, 

 it is said, to the secreting cells also. 



The structure of the elementary portions of a secreting 

 apparatus, namely epithelium, simple membrane, and 

 blood-vessels, having been already described in this and 

 previous chapters, we may proceed to consider the manner 

 in which they are arranged to form the varieties of 

 secreting glands. 



SECRETING GLANDS. 



The secreting glands are the organs to which the office 

 of secreting is more especially ascribed : for they appear to 

 be occupied with it alone. They present, amid manifold 

 diversities of form and composition, a general plan of 

 structure, by which they are distinguished from all other 

 textures of the body ; especially, all contain, and appear 

 constructed with particular regard to the arrangement of, 

 the cells, which, as already expressed, both line their tubes 

 or cavities as an epithelium, and elaborate, as secreting 

 cells, the substances to be discharged from them. 



For convenience of description, they may be divided into 

 three principal groups, the characters of each of which are 

 determined by the different modes in which the sacculi or 

 tubes containing the secreting cells are grouped : 



I. The simple tubule, or tubular gland (A, fig. 105), exam- 

 ples of which are furnished by the several tubular follicles 

 in mucous membranes : especially by the follicles of Lie- 

 berkiihn in the mucous membrane of the intestinal canal 

 (p. 300), and the tubular or gastric glands of the stomach 

 (p. 268). These appear to be simple tubular depressions of 

 the mucous membrane on which they open, each consisting 

 of an elongated gland-vesicle, the wall of which is formed 

 of primary membrane, and is lined with secreting cells 

 arranged as an epithelium. To the same class may be 



D D 



