968 



THE INTERNAL SECRETIONS 



aorta by two or three small branches, and from the phrenic and renal 

 arteries.^ It is also of importance to remember that each gland 

 rests upon a ramification of sympathetic fibers which is known as the 

 suprarenal plexus, and which communicates centrally by way of the 

 greater and lesser splanchnic nerves (Fig. 226) with the sjrmpathetic 

 ganglia of the thorax and lumbar region. Peripherally, each supra- 

 renal plexus is connected with the mesenteric and celiac ganglia of 

 the solar plexus. 



The right gland has a flattened, triangular outline, while the left is crescentic, 

 its concavity being directed toward the neighboring kidney. In man, each gland 

 measures about 3 cm. from side to side, 3-5 cm. from above downward and 4-6 

 mm. in thickness. Their weight varies between 4 and 7 grams, the left one being 



Fig. 507. — Diagram to Illustrate the Position or the Adrenal Glands (Rabbit). 

 K, kidneys; V, ureters; RV, renal veins; RA, renal arteries; JC, inferior vena cava; 

 A, abdominal aorta; S, adrenal glands; SU, suprarenal veins. In man, the two kidneys 

 lie very nearly in the same horizontal plane; in fact, the right organ frequently below 

 the left. 



slightly heavier than the right. When cut into, each gland exhibits an outer 

 cortical and an inner medullary region. The former is divided into compartments 

 by a fibrous stroma derived from the outer fibrous investment. These spaces are 

 occupied by numerous columns of intercommunicating cells which are roughly 

 arranged in the form. of a reticular and glomerular zone. The yellowish globules 

 (lipoids) contained in these cells, are responsible for the peculiar yellowish-pink 

 color of the entire gland. The medulla is pervaded by a stroma, enclosing groups 

 of granular cells, which on treatment with chromic acid acquire a yellowish brown 

 color. On account of their power of reducing this substance, they are commonly 

 designated as chromophil or chromaffine cells. We also find here numerous nerve 

 cells, some smooth muscle tissue, and large venous capillaries supported by fibrous 

 tissue. These structural differences are in complete agreement with the develop- 

 ment of this organ, because while the cortex is derived from that part of the 

 mesoblast which gives rise to the mesonephros, the medulla is formed from an 

 outgrowth of the sympathetic system. Besides, these two constituents of the 

 adrenal body remain absolutely separate in some of the lower vertebrates, the 



1 Gerard, Jour, de I'anat. et de la physioL, 1913. 



