1058 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



tains 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 con- 

 tinuous 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. Imme- 

 diately 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 Hensen's 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 pha- 

 langes, 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 laminae 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 Hensen's stripe, due to the intercrossing of its fibers. 

 The lateral margin of the membrane is much thinner. Hardesty 1 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 

 ampullae 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 ampullae 

 of the superior and lateral semicircular ducts; those of the inferior branch traverse 



1 American Journal of Anatomy, 1908, viii. 



2 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. 





