Integrative Systems 



219 



mm 





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fe 



& 



Fig. 186. Adrenal gland, human. (Top) Section through the zona fasciculata. 

 (Bottom) Section of medulla. (Courtesy, Bremer: "Text-Book of Histology," 

 Philadelphia, The Blakiston Company.) 



the medulla and the nature of its secretion justify regarding it as 

 being virtually an autonomic ganglion whose exciters, lacking post- 

 ganglionic conductor-fibers and possessing exaggerated secretory 

 capacity, broadcast their stimulating substance to their distant effec- 

 tors via the blood-stream instead of giving them individual service 

 through nerve-fibers. Consistent with this interpretation, the auto- 

 nomic fibers directly related to the medullary cells are described as 

 being preganglionic. If they are, it puts the secreting cells in the 

 position of exciter (postganglionic) neurons. 



The endocrinal glands derived from the pharynx resemble 

 those of the adrenal group in respect to their number and degree of 



