24 ANATOMY 



breadth, and 2 to 8 mms. in thickness, except at the bases 

 where they are twice as thick. The medulla makes up about 

 10 per cent of the weight of the glands. 



Circulation. The blood supply of the adrenal is peculiar in 

 several respects. 201 • 213 There is a separate arterial supply to 

 the cortex and medulla. The cortex, however, has no marked 

 venous system, the blood being drained into the capillary 

 network of the medullary arteries and ultimately drained 

 by the well developed venous system of the medulla. The 

 transition of the arterial network of the cortex to that of the 

 medulla occurs in the reticular zone in which is found an 

 exceedingly fine capillary system with very narrow meshes 

 each of which appears to surround a single cell. It has not 

 been established if this network consists of closed capillaries 

 or of unwalled spaces. The adrenal cortical capillaries behave 

 on vital staining like the reticuloendothelial cells of the spleen, 

 liver, etc. in which loosely built or interrupted capillary sys- 

 tems are found. 10 



Aside from the above described circulation there is a second 

 venous circulation of the cortex in which tiny branches from the 

 left adrenal (possibly also from the right) communicate with 

 branches of the splenic and pancreatic veins and thus with the 

 portal system. 



The arterial blood reaches the adrenals through channels 

 derived from the aorta, the inferior phrenic, and the renal 

 arteries. Three arteries, one of which supplies the medulla, 

 penetrate into the capsule and break up into capillaries which 

 end in the venous plexus of the medulla. The adrenals are 

 richly vascularized. Houssay and Molinelli 315 observed a blood 

 flow of 0.35 cc. per minute per kilo of body weight in dogs. 

 Neumann found the blood flow through the adrenals to ex- 

 ceed that of any other organ, viz., 6 to 7 cc. per gram of 

 adrenal tissue per minute. Subsequent workers have found 

 smaller blood flows. 545 



The great muscular content of the adrenal vein is striking. 



