DEVELOPMENT OF SUPRARENAL BODIES IN MAMMALIA. 79 



in the mesh. These cells are collected into groups by coarser 

 trabeculae, and the forms these cell groups assume in different 

 layers give characteristic appearances to any particular layer. 

 We thus recog-nise in the suprarenals of the rabbit three 

 distinct zones {a, b, c, fig. 1), which correspond to the 

 three layers visible to the naked eye (see above). The outer- 

 most zone (a) shows cell groups in long radiating columnar 

 rowSj which, directly under the capsule, form small arches, 

 as shown in the figure. The cells are more closely packed 

 than in the middle zone. Between the columns are rather 

 large, longish spaces {w, w), which are shown to be sections 

 of blood-vessels by the endothelial cells lining them. This 

 zone gradually passes into the inner {b), where the columns 

 are shorter and thicker, and cells are not as closely packed. 

 This zone forms, in most sections^ by far the largest portion 

 of the cortical substance. Its cells stand out beautifully 

 Between the columns there may be seen, running radially, fine 

 capillary blood-vessels, shown to be such by their endothelial 

 cells. The innermost zone (c) has irregular cell groups, and 

 is characterised by the presence of a great many blood-vessels 

 (v, V, v). The latter, becoming larger and larger toward the 

 centre by the union of numerous branches, finally open into 

 the central large veins, found in the medullary substance, 

 which, in their turn becoming one, leave the organ at its 

 posterior end. 



I may remark in passing that the two inner zones men- 

 tioned above correspond to the zona reticularis and zona 

 fasciculata of Arnold,^ but the outermost is different from 

 his zona glomerulosa, as the cell groups are oval in the 

 latter. 



In sections cut with a freezing microtome from a fresh 

 suprarenal, the whole cortical part is so filled with fat-like 

 globules that it is hard to see anything else. These fat-like 

 globules are not stained by osmic acid, and therefore do not 

 seem to be true fat. In the process of hardening in picric 

 and chromic acids and other reagents, except alcohol, they 

 disappear completely. Even with specimens hardened in 

 alcohol they seem to be lost in the process of embedding in 

 wax. 



The medullary cells are collected into oval or roundish 

 groups by network of connective tissue, and I have not suc- 

 ceeded in seeing any one cell distinctly. The groups look 

 like a collection of nuclei embedded in a mass of protoplasm. 

 This alone would separate them from the cortical cells, each 

 of which, as has been remarked, is placed in a special mesh 

 1 ' Virchow's Archiv,' 1866. 



