ADRENAL GLANDS The adrenal glands or suprarenal capsules are two conical bodies, flattened from before backward, resting on the upper poles of the kidneys close to the sides of the vertebral column ; each has a concave base which is in contact with the kidney. On the anterior surface is a transverse sulcus or hilum from which a large vein emerges. The arteries are less constant in their points of entry. The glands are entirely retro-peritoneal. In a vertical transverse section each gland is seen to consist of two parts, cortical (yellow) and medullary (red). The cortical substance is composed of columns of cells, separated by a stroma. The medullary part con sists of small islets of cells, which resemble columnar epithelium lying among venous sinuses; these cells are in close connection with the sympathetic nerve filaments from the great solar plexus.
The generally accepted view is that the corti cal substance is derived fom the coelomic epithelium covering the mesoderm of the upper (cephalic) portion of the Wolffian body, and corresponds to the nephrostomes of mesonephridial tubules (see URINARY SYSTEM), while the medullary part grows out from the sympathetic ganglia and so is probably ectodermal in origin. In the early human embryo the adrenals are larger than the kid neys, and at birth they are proportionately much larger than in the adult.
Adrenals are unknown in Am phioxus and the Dipnoi. In the Cyclostomata (hags and lampreys) they are said by some to arise in connection with the cephalic part of the pronephros, though other writers deny their presence altogether. In the Elasmobranchs and Holocephali the medul lary and cortical parts are apparently distinct, the former being represented by a series of organs situated close to the intercostal arteries, while the latter may be either median or paired, and, be ing placed between the kidneys, are often spoken of as interrenals. In the Amphibia the glands are sunk into the surface of the kid ney. In reptiles and birds they are long lobulated bodies lying close to the testis or ovary. In the lower mammals they are not as closely connected with the kidneys as they are in man, and their shape is usually oval or spherical.
