44 



PHYSIOLOGY 



CHAP. 



in that case atrophy after birth, whereas their growth continues, 

 though very slowly, till the adult age (Brown-Sequard). 



In section, the fibrous sheath is succeeded by a broad cortical 

 layer, hard, striated in appearance, and dark yellow, which forms 

 the principal mass of the gland, and an inner, medullary part, 

 soft and brownish in colour : the older anatomists took this to be 

 a dense secretion collected in a cavity, from which they incorrectly 

 designated the whole organ a capsule (Fig. 10, A). 



From the fibrous sheath, which often contains plain-muscle 

 cells (Fusari), fine septa or trabeculae are given off into the 

 organ, and serve as a framework which supports the columns 



of polyhedral epithelium 

 cells. 



Three zones can be dis- 

 tinguished in the cortex, 

 better in some other animals 

 than in man, which are differ- 

 ^ entiated by the arrangement 

 of the epithelium cells : these 

 ^ are known as the zona 

 glomerulosa, the zona fasci- 

 culata, and the zona'reticu- 

 laris (Fig. 10, B). 



The medulla is separated 

 from the cortex by a sheet of 

 loose connective tissue. It 

 is composed of a network, 

 the meshes of which enclose 



FIG. 11. Medullary substance of suprarenal body of poll pnlnrnnq whinh rliffpr 



ox, stained haematoxylin. (Vassale.) a, resting ^ ei HUM, WniC 



cells ; 6, cells in active function, filled with irom those of the COrteX in 



chromaffine substance which is discharged directly i i i i 



. into the blood capillaries. being larger, less granular, 



more irregular in form, and 



vacuolated, and they stain a brown colour with solutions of 

 chromic acid and its salts, while the cortical cells give hardly 

 any such reaction. Owing to this specific property the medullary 

 cells have been termed chromaffine or chromaphile (Kohn), a term 

 now frequently used to distinguish the medullary from the 

 cortical substance (Fig. 11). 



The difference between the two parts of the adrenal glands 

 is not confined to this histological peculiarity. According to 

 recent work in embryology and comparative anatomy, the 

 medullary and the cortical substance represent two perfectly 

 distinct and independent organs, which in the majority of verte- 

 brates fuse together during foetal development, and apparently 

 form only one single organ. In the Elasmobranchs, on the 

 contrary, the two organs remain separate during the whole of the 

 animal's life. Balfour (1877) showed that these fishes have no 



