The blood vessels of the limbus spiralis.

The capillaries of the spiral limbus in the cochlea of the laboratory rat were investigated under light and electron microscopy. A stereological examination of the capillary volumes of specimens injected with horseradish peroxidase was performed. The volume of capillaries amounted to 2.87%, and, as such, is very high. The ultrastructure of the capillaries showed continuous endothelial cells and basal laminae, discontinuous pericytes and varying relations towards the surrounding tissue. Morphological criteria, such as microvilli and plasmalemmal vesicles, suggest a significant transendothelial transport. The causes for the abundance of vessels in the spiral limbus are discussed: the transport of oxygen to the perilymph and the need of substances for the formation of the tectorial membrane seem to be important factors. The transport processes are obviously controlled by the endothelial cells as well as by the spiral limbus cells.