CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 765 



alveoli separated by septa of vascular connective tissue. Though 

 in some instances the alveoli of the pituitary body like those of 

 the thyroid possess a lumen, which moreover may hold more or 

 less 'colloid' contents, the majority are solid masses of epithelial 

 cells. The cells, which are columnar or polyhedral, present no 

 special characters, except perhaps that between the usual epithe- 

 lial cells are occasionally found spindle-shaped cells, apparently of 

 mesoblastic origin. 



Concerning the processes which take place in these alveoli and 

 the purposes of the organ as a whole we know absolutely nothing. 



497. The Suprarenal Bodies. A (mammalian) suprarenal 

 body when cut across is seen to consist of two distinct parts, an 

 outer thicker cortical part, of yellowish colour, striated radially, 

 and an inner thinner medullary part of darker colour. At the 

 depression on the anterior surface called the hilus, whence issues 

 the comparatively large suprarenal vein, the cortex thins away so 

 that the medulla comes to the surface. These two parts, cortex 

 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 blood vessels; and in some animals 

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

 suprarenals 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 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 



