TTTE SUPRARENAL GLANDS 



555 



plexus through the intercellular ret iciiluni of the /.<>na fasciculata, where 

 llicv are in intimate relation with the epithelial cells, and reach (he /ona 

 reticiilaris. Here the capillaries are collected into thin-walled venules 

 or sinusoids. These vessels, after some anastomoses, form venous stems 

 which are continued, without further anastomosis, through the medulla 

 to the central veins. The venules of the cortex possess no walls other 

 than their endotheliuin. 



The medullary arteries are also derived from the capsular plexus. 

 They penetrate the cortex, and at the border of the medulla abruptly 



FIG. 481. RECONSTRUCTION OF A DOG'S ADRENAL. 

 a, arteries; v, vein. X 25. (After Flint.) 



terminate in a plexus of capillary vessels which lie in the connective 

 tissue stroma and come into intimate relation with the medullary cells. 

 These vessels possess extremely thin walls, their eiidothelium often being 

 in direct contact with the adjacent epithelium, whose cells frequently im- 

 pinge upon the lumen of the capillary vessel (see Fig. 4S1). The capil- 

 lary plexus pervades the entire medulla, its vessels being here and there 

 collected into small venules which unite to form the central veins. 

 These form two, or sometimes four, main stems (Flint) which make 

 their exit at the hilum and enter the lumbar or renal vein, or, on the 

 riidit side, enter the inferior vena cava. 



O 



All of the efferent veins of the adrenal are characterized by a peculiar 

 distribution of their smooth muscle fibers, which occur in considerable 

 abundance, but are nearly all disposed in the axis of the vessel; the 



