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outer; the two rows incline toward each other and, coming into contact above, enclose between them and the basilar membrane a triangular tunnel, the tunnel of Corti. On the inner side of the inner rods is a single row of hair cells, and on the outer side of the outer rods three or four rows of similar cells, together with certain supporting cells termed the cells of Deiters and Hensen. The free ends of the outer hair cells occupy a series of apertures in a net-like membrane, the reticular membrane, and the entire organ is covered by the tectorial membrane.
  RODS OF CORTI.—Each of these consists of a base or foot-plate, and elongated part or body, and an upper end or head; the body of each rod is finely striated, but in the head there is an oval non-striated portion which stains deeply with carmine. Occupying the angles between the rods and the basilar membrane are nucleated cells which partly envelop the rods and extend on to the floor of Corti’s tunnel; these may be looked upon as the undifferentiated parts of the cells from which the rods have been formed.

FIG. 932– The lamina reticularis and subjacent structures. (Schematic.) A. Internal rod of Corti, with a, its plate. B. External rod (in yellow). C. Tunnel of Corti. D. Membrana basilaris. E. Inner hair cells. 1, 1’. Internal and external borders of the membrana reticularis. 2, 2’, 2”. The three rows of circular holes (in blue). 3. First row of phalanges (in yellow). 4, 4’, 4”. Second, third, and fourth rows of phalanges (in red). 6, 6’, 6”. The three rows of outer hair cells (in blue). 7, 7’, 7”. Cells of Deiters. 8. Cells of Hensen and Claudius. (Testut.) (See enlarged image)

  The inner rods number nearly 6000, and their bases rest on the basilar membrane close to the tympanic lip of the sulcus spiralis internus. The shaft or body of each is sinously curved and forms an angle of about 60 degrees with the basilar membrane. The head resembles the proximal end of the ulna and presents a deep concavity which accommodates a convexity on the head of the outer rod. The head-plate, or portion overhanging the concavity, overlaps the head-plate of the outer rod.
  The outer rods, nearly 4000 in number, are longer and more obliquely set than the inner, forming with the basilar membrane an angle of about 40 degrees. Their heads are convex internally; they fit into the concavities on the heads of the inner rods and are continued outward as thin flattened plates, termed phalangeal processes, which unite with the phalangeal processes of Deiters’ cells to form the reticular membrane.

Hair Cells.—The hair cells are short columnar cells; their free ends are on a level with the heads of Corti’s rods, and each is surmounted by about twenty hair-like processes arranged in the form of a crescent with its concavity directed inward. The deep ends of the cells reach about half-way along Corti’s rods, and each contains


