Sustentacular cells of the organ of Corti--the tectal cells of the outer tunnel.

The cells which form the roof of the outer tunnel of the organ of Corti were studied by light microscopy and scanning and transmission electron microscopy. In the mustache bat, Pteronotus p. parnellii, the cells are characterized by: (1) a unique position in the roof and along the lateral wall of the outer tunnel; (2) no contact with the basilar membrane; (3) isolation of adjacent cell bodies; (4) an extensive endolymphatic surface with a sparse population of short microvilli; (5) a loose association with the adjacent mat of polypous surface projections on the outer tunnel surface of the first row of Hensen's cells; and (6) a darkly staining cytoplasm. These cells occur in certain other mammals (cats and mice) and have been classified previously as Hensen's or Deiters' cells, but since they lack the distinct morphological characteristics of either of these types of cells, it is suggested that they be recognized as a distinct cell type, the tectal cells of the outer tunnel.