THE SUPRARENAL SYSTEM 271 



more delicate and, in the neighbourhood of the medulla, they 

 break up into a line net, composed of the finest connective tissue 

 threads (zona reticularis, Arnold), in the meshes of which single 

 parenchyma cells are situated. At the boundary between medulla 

 and cortex there are again a certain number of thicker connective 

 tissue threads running tangentially. 



The fans formed by the lamellae of connective tissue are 

 divided into meshes of different sizes by delicate septa running 

 transversely and diagonally. These meshes contain the cortical 

 cells, not as Ecker described them, in the form of bladders or 

 tubules, but, both in man and in animals, in typical, solid cell- 

 columns without cavity the cortical cylinders of Kollicker. These 

 cell-columns are usually composed of a single row 7 of cells, though 

 occasionally of two or three; they traverse the external layer either 

 directly or in a winding fashion, and end in the transverse con- 

 nective tissue processes, or they may curve back like an arch and 

 terminate in one another. In the median layer, these cell-cylinders 

 are arranged in drawn-out radiating columns, in accordance with 

 the shape of the meshes formed by the longitudinal connective 

 tissue threads. In the interior, the columns break up into a net- 

 work formed by single rows of cells, in the meshes of which the 

 tine capillaries are situated. The meshes of the network, which 

 at first are rounded, become flattened radially as they approach 

 the medulla. 



The form and size of the cells in the individual layers, varies 

 with the changes in the arrangement of the connective tissue struc- 

 ture and of the cell columns. The cells in the external zone are, 

 upon the whole, small in size and are of various shapes. In the 

 human suprarenal these cells are mostly polygonal ; in tangential 

 sections they appear in the form of rounded balls and cell nests 

 enclosed in connective tissue. The cells in the median layer are 

 larger in size ; in form, they are rounded polygons which are 

 occasionally elongated in the direction of the column ; and they 

 are arranged several together, side by side, transversely of the 

 column. As they approach the internal layer, the cells become 

 smaller in size and either cubic or polyhedral in form; while the 

 cells in the innermost cylinders are frequently oblong. 



The connective tissue which runs between the cortical cell 

 cylinders carries numerous capillaries and veins. These vessels 

 pass between the cell columns and are somewhat dilated in the 

 outer layer; they are especially numerous in the internal zone. 

 Actual main arteries are not present in the cortex. The cortical 

 cells are placed directly against the thin vessel walls, which are 

 composed of endothelium and are sometimes enclosed in a delicate 

 connective tissue membrane. 



The arrangement of the cortical parenchyma is, in the main 

 points, the same in all mammals, though the form, size and 

 arrangement of the cells varies. In many species the zona 



