[Ultrastructural study of the median eminence of the cat].

The electron microscopic study of the median eminence in cats sacrified during the growth period (36 hours to 30 days after-birth) and in adult cats leads to the following conclusions: 1) The external infundibular zone of newborn kittens (36 hours postpartum) shows very few capillary loops and it lacks a palissade appearance. On the seventh day a palissade layer and penetrating capillary loops are observed. 2) There are no myelinated fibers in the fibrillar layer of the median eminence external infundibular zone during the growth-period. The number and size of Herring bodies increase after the seventh day. In adult cats, Herring bodies may be 50 microns long and some show myelinic sheaths. 3) In adult cats, the nerve endings which surround the capillary loops penetrating into the median eminence, are in direct contact with the lamina basalis, while the nerve endings of the palissade layer are always separated from the capillary space of the hypophyseal portal plexus by glial cell prolongations.