Henry Gray (18251861). Anatomy of the Human Body. 1918.
a large nucleus; in contact with the deep ends of the hair cells are the terminal filaments of the cochlear division of the acoustic nerve. The inner hair cells are arranged in a single row on the medial side of the inner rods, and their diameters being greater than those of the rods it follows that each hair cell is supported by more than one rod. The free ends of the inner hair cells are encircled by a cuticular membrane which is fixed to the heads of the inner rods. Adjoining the inner hair cells are one or two rows of columnar supporting cells, which, in turn, are continuous with the cubical cells lining the sulcus spiralis internus. The outer hair cells number about 12,000, and are nearly twice as long as the inner. In the basal coil of the cochlea they are arranged in three regular rows; in the apical coil, in four, somewhat irregular, rows.
Between the rows of the outer hair cells are rows of supporting cells, called the cells of Deiters; their expanded bases are planted on the basilar membrane, while the opposite end of each presents a clubbed extremity or phalangeal process. Immediately to the outer side of Deiters cells are five or six rows of columnar cells, the supporting cells of Hensen. Their bases are narrow, while their upper parts are expanded and form a rounded elevation on the floor of the ductus cochlearis. The columnar cells lying outside Hensens cells are termed the cells of Claudius. A space exists between the outer rods of Corti and the adjacent hair cells; this is called the space of Nuel.
The reticular lamina(Fig. 932) is a delicate frame-work perforated by rounded holes which are occupied by the free ends of the outer hair cells. It extends from the heads of the outer rods of Corti to the external row of the outer hair cells, and is formed by several rows of minute fiddle-shaped cuticular structures, called phalanges, between which are circular apertures containing the free ends of the hair cells. The inner most row of phalanges consists of the phalangeal processes of the outer rods of Corti; the outer rows are formed by the modified free ends of Deiters cells.
Covering the sulcus spiralis internus and the spiral organ of Corti is the tectorial membrane, which is attached to the limbus laminæ spiralis close to the inner edge of the vestibular membrane. Its inner part is thin and overlies the auditory teeth of Huschke; its outer part is thick, and along its lower surface, opposite the inner hair cells, is a clear band, named Hensens stripe, due to the intercrossing of its fibers. The lateral margin of the membrane is much thinner. Hardesty1 considers the tectorial membrane as the vibrating mechanism in the cochlea. It is inconceivably delicate and flexible; far more sensitively flexible in the transverse than in the longitudinal direction and the readiness with which it bends when touched is beyond description. It is ectodermal in origin. It consists of fine colorless fibers embedded in a transparent matrix (the matrix may be a variety of soft keratin), of a soft collagenous, semisolid character with marked adhesiveness. The general transverse direction of the fibers inclines from the radius of the cochlea toward the apex.
The acoustic nerve (n. acusticus; auditory nerve or nerve of hearing) divides near the bottom of the internal acoustic meatus into an anterior or cochlear and a posterior or vestibular branch.
The vestibular nerve (n. vestibularis) supplies the utricle, the saccule, and the ampullæ of the semicircular ducts. On the trunk of the nerve, within the internal acoustic meatus, is a ganglion, the vestibular ganglion (ganglion of Scarpa); the fibers of the nerve arise from the cells of this ganglion. On the distal side of the ganglion the nerve splits into a superior, an inferior, and a posterior branch.2 The filaments of the superior branch are transmitted through the foramina in the area vestibularis superior, and end in the macula of the utricle and in the ampullæ of the superior and lateral semicircular ducts; those of the inferior branch traverse
Note 1. The nerve sometimes splits on the proximal side of the ganglion, and the latter is then divided into three parts, one on each branch of the nerve. [back]
Note 2. Whipple, Inez L., The Ventral Surface of the Mammalian Chiridium, etc., Zeit. f. Morph. u. Anthropol 1904, vol. vii. [back]