ANATOMY, EMBRYOLOGY AND HISTOLOGY 61 



containing glomerular, fasicular, and reticular zones, as well as charac- 

 teristic medullary tissue. 



Blood Supply of the Suprarenals. The adrenal is said to be rela- 

 tively the most vascular organ in the body, receiving about six times its 

 weight of blood per minute. The blood supply usually springs from three 

 sources. The superior suprarenal artery arises from the inferior phrenic 

 artery, the middle suprarenal from the aorta, and the inferior suprarenal 

 from the renal artery. All three anastomose freely. The branching of the 

 arteries within the glands is fully described by Flint. The capillaries are 

 large and sinusoidal, that is to say, they are as large as venules, but 

 possess only endothelial walls. They pass into veins, receiving tributaries 

 from the capsule, cortex and medulla, which run together forming the 

 central vein of the gland which emerges at the hilus. Each suprarenal 

 is also surrounded by a rich venous plexus which communicates with a 

 similar network about the kidney. On the left, the plexus discharges into 

 the renal vein, and on the right, into the inferior vena cava. 



Lymphatics. The lymphatics are also abundant. Their close associa- 

 tion with the secreting cells has been studied by Kumita. They form a 

 rich network in the medulla, which communicates, through the cortex, with 

 a subcapsular network. Lymph is discharged into the lymph glands along 

 the aorta. There is also a variable but important connection, on the left 

 side, with the posterior mediastinal glands. 



Innervation. The nerve supply of the glands is but little understood. 

 It is known, however, that they receive their chief innervation directly 

 from the splanchnics (Eig. 2). Fibers from, the suprarenal plexus 

 enter them. Assertions to the effect that they receive twigs from the vagi 

 and phrenics are probably erroneous. The splanchnics carry myelinated 

 preganglionic fibers, arising from cells in the lateral column of the spinal 

 cord, as well as postganglionic fibers from cells in the thoracic ganglia. 

 According to Falta(rf), the right suprarenal in rabbits is supplied by the 

 right and left splanchnics, while the left is innervated by the right splanch- 

 nic only. It is not known whether there is any difference between the 

 two in man. The fibers from the suprarenal plexus are probably all 

 postganglionic and unmyelinated. Coming from these sources, they form 

 a network in the connective tissue surrounding the organ and then pene- 

 trate into it, running in the connective tissue septa between the cell 

 columns in the cortex. Their subsequent behavior has not been worked 

 out in detail. Groups of sympathetic cells occur normally in the medulla, 

 and occasionally in the cortex, with which they come into relation. We 

 have reason to believe that fibers terminate about the blood vessels and in 

 contact with the secreting cells in both the cortex and the medulla. Ac- 

 cording to Burton-Opitz and Edwards, the evidence advanced in favor of 

 the existence of vasodilator fibers is not sufficiently convincing. 



