44 ANATOMY 



the Primates and Ungulates. In man the cells of the fascicu- 

 lata are filled with fine granules and droplets consisting of 

 cholesterol ethers. During childhood this zone is narrow but 

 after puberty the columns are long, two or three cells in width, 

 and closely packed (Figure 5). In late life, the columns be- 

 come shorter and less closely packed. 123 



The outer portion of the fasciculata in man has also been 

 denoted as the "spongy zone" while the inner portion has 

 been referred to as the "siderophile zone" because of the ap- 

 pearance of certain cells in this region. 231 These siderophile 

 cells, which possibly represent exhausted cells, are most promi- 

 nent in the guinea pig (Cavia cobaya)™ 1 



The zona reticularis, or innermost layer of the cortex mani- 

 fests the most diverse cytological appearances in different 

 species. It is the zone in which degenerative changes occur 

 and hence its appearance will depend on the rate at which the 

 cells of the adrenal in a given species are being renewed. 



In man, the cells of the zona reticularis contain fine droplets 

 of lipid as do also the endothelial cells of the blood capillaries 

 within the reticular layer. The reticular layer of the human 

 adrenal is also characterized after the second decade of life by 

 the presence of a pigment which increases in amount with age. 

 This pigment is usually considered as analogous to the "wear 

 and tear" pigment observed in other organs. It has no special 

 significance or relation to the pigmentation of Addison's dis- 

 ease as was formerly believed. In man the reticularis is 

 clearly differentiated from the fasciculata by the arrangement 

 of its cells and its rich blood supply. It is more open in tex- 

 ture than the medulla (c/. Figure 5). The cells of the reticular 

 zone are the largest in the cortex. They are rounded and 

 well-defined with a coarsely granular and finely vacuolated cy- 

 toplasm. The zona reticularis becomes wider and more vascu- 

 lar as age advances. In late life it may equal the fascicular 

 zone in width. 123 



In the guinea pig the zona reticularis appears speckled due 



