SUMMARY The internal anatomy, particularly the vasculature, of the human adrenal was investigated with the help of three-dimensional reconstruction models supplemented by stereo-angiography. A definite pattern of positional relationship was shown to exist between the cortex, medulla and venous drainage, and on this basis the adrenal should be considered as a tripartite structure consisting of a head, a body and a tail region. The disposition of the longitudinal muscle bundles in the adrenal veins follows a definite pattern in each region of the gland. The muscular veins lie almost entirely within sleeves of cortical tissue. The selective gathering of the muscle bundles into the medulla-facing segment of the veins in certain regions of the gland is described. The effect of this muscular arrangement on the venous sinuses which pass between the muscle bundles was investigated and considered to be one of closure. Elastic tissue was demonstrated in the medullary venous sinuses; it is suggested that together with the muscle bundles both constitute a musculo-elastic organ capable of intermittent explosive release of hormones from the venous sinuses into the central vein. The hitherto neglected effect of the unique venous sytem on the function of the cortex was examined. Its possible role in the morphological changes of the adult cortex in response to stress, adrenocorticotrophic hormone, and in adrenal pathology is considered.

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