The imposing size of the adrenal bodies in the human fetus and in the newly born infant has long attracted the attention of anatomists. The first detailed histologic description of the involutional process whereby these glands are converted into the mature but relatively smaller organs of childhood and adult life was published by Thomas1 in 1911. In an investigation of the response of the adrenal glands during infections, Thomas called attention to the fact that these structures normally undergo extensive morphologic reorganization during the first year of life: The inner zone of the cortex (zona reticularis), which is relatively wide and conspicuously hyperemic at birth, suffers complete degeneration and is encroached on and replaced by the rapidly growing medullary portion of the gland. More exact information concerning the details of the maturation of the adrenal glands was contributed by the researches of Kern,2 Kawamura,3 Landau,4 Lewis