CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 801 



The whole organ is surrounded by a capsule of connective 

 tissue, free from muscular fibres and not very rich in elastic 

 elements. From the capsule septa pass inwards and form a 

 frame-work, the cavities of which are filled by cells or groups of 

 cells differing in nature and differently arranged in the cortex and 

 in the medulla. The middle larger part of the cortex is composed 

 of somewhat long solid columns of polyhedral cells, lodged in 

 corresponding meshes of the frame-work. The columns, which 

 are three or four cells thick and several cells in length, though 

 somewhat irregular and varying in size, do not anastomose, being 

 wholly separated from each other by the bars of connective tissue, 

 and possess no central cavity or lumen. The blood vessels which 

 are abundant in these bars of connective tissue do not penetrate 

 the columns. The cell-substance of the cells is of a yellowish 

 colour, often containing yellowish oil globules, and possesses a clear 

 round nucleus. 



In the outer part of the cortex immediately underneath the 

 capsule is a thin zone in which the groups of cells are not columnar 

 but rounded and irregular; and again in the inner part of the 

 cortex abutting on the medulla is another thin zone, in which 

 the columnar arrangement is lost, the cells being here disposed 

 in a network of thin cords and the individual cells to a large 

 extent separated from each other by delicate continuations of the 

 coarser connective tissue septa. Hence the main median part 

 of the cortex, which from the prominent columnar arrangement 

 appears striated radially, is often called the zona fasciculata, the 

 thin outer part the zona glomerulosa, and the thin inner part the 

 zona reticularis ; but so far as the essential characters of the cells 

 are concerned all the three zones are alike. 



The medulla also consists of cells or groups of cells lying in 

 the meshes of a connective-tissue frame-work, but the cells are of 

 a different nature from those of the cortex. They are irregular 

 and often branched, and their cell-substance, though it sometimes 

 contains pigment, is generally clear and transparent. The medulla 

 moreover is further distinguished from the cortex by the abundant 

 supply of blood vessels and of nerves. 



The cells of the medulla and of the inner zone (zona reticularis) 

 of the cortex are very apt to undergo change after death, and to 

 become diffluent. 



The arteries which come from the aorta and from the renal and 

 phrenic arteries pass into the organ on the surface, and traversing 

 the cortex, supplying as they go both capsule and cortex with a 

 moderate number of vessels, end in the medulla, the connective- 

 tissue bars of which bear numerous large venous sinuses, into 

 which the capillaries pour their blood, and from which the blood 

 is gathered up into the suprarenal vein; the very thin walls 

 of these venous sinuses are close set with the cells of the 

 medulla. 



