468 THE METABOLIC PROCESSES OF THE BODY. 



dilation in the brain. But the exact nature of this influence has not 

 been made clear. 



410. The pituitary body. The lower, posterior, lobe of this organ 

 resembles the thyroid body (the upper, anterior, lobe is of quite distinct 

 nature, being really a part of the central nervous system). 



Concerning the processes which take place in these alveoli, and the pur- 

 poses of the organ as a whole, we know absolutely nothing. 



411. The supra-renal bodies. A (mammalian) supra-renal body, when 

 cut across, is seen to consist of two distinct parts, an outer thicker cortical 

 part, of yellowish color, striated radially, and an inner thicker medullary 

 part of dark color. At the depression on the anterior surface called the 

 hilus, whence issues the comparatively large supra-renal vein, the cortex 

 thins away so that the medulla comes to the surface. These two parts, cor- 

 tex and medulla, are not, like the cortex and medulla of a lymphatic gland, 

 different arrangements of the same material, but are of essentially different 

 nature, and, indeed, are of different origin. The medulla is derived from, is 

 a modification of, sympathetic ganglia, while the cortex is derived from 

 masses of mesoblastic cells surrounding the great bloodvessels ; and in some 

 animals the two form wholly separate bodies. The so-called accessory supra- 

 renals are composed of cortex alone. 



The whole organ is surrounded by a capsule of connective tissue, free 

 from muscular fibres, and not very rich in elastic elements. From the cap- 

 sule septa pass inward and form a framework, 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 framework. 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 bloodvessels, which are abundant in these bars of connective tissue, do 

 not penetrate the columns. The cell substance of the cells is of a yellow- 

 ish color, 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 as far as the essential cha- 

 racters 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 framework, 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 bloodvessels 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, supply- 



