AUDITORY NERVE. 123 
The lamina reticularis is a thin cuticular structure, which lies over Corti’s organ 
aud extends from the heads of the outer rods as far as Hensen’s cells, where it ends in a 
row of quadrilateral areas, which form its outer border. On looking at it from above, it is 
seen to consist of two or nee rows of structures, named phalanges, which are elongated 
cuticular plates, resembling in shape the digital phalanges. The innermost row is formed 
by the phalangeal processes of the heads of the outer row of Corti’s rods; the succeeding 
row, or rows, represent the expanded upper ends of Deiters’ supporting cells. The number 
of rows of phalanges, therefore, varies with the number of rows of outer hair cells and the 
alternating cells of Deiters. The phalanges separate the free ends of the hair cells from 
each other, since these are seen to occupy the somewhat circular apertures between their 
constricted middle portions. 
The membrana tectoria (Mig. 528) is an elastic membrane overlying the sulcus spiralis 
internus and the organ of Corti. Attached, by its inner end, to the limbus laminz spiralis, 
near the lower edge of Reissner’s membrane, it reaches outwards as far as the outer row of 
hair cells. Its inner portion is thin and overlies the auditory teeth of Huschke. — Its 
outer part is, at first, much thickened, but becomes attenuated near its external border, 
which, according to Retzius, is attached to the outer row of Deiters’ cells. Its lower edge 
presents a firm, homogeneous border, and opposite the inner row of hair cells contains a 
clear, spirally-arranged band, named Hensen’s stripe. Probably the membrana tectoria 
acts as a damper comparable to the otoconia in the utricle and saccule. 
Auditory Nerve (Fig. 529).—The auditory nerve divides into two main parts, 
the ramus vestibularis and the ramus cochlearis ; as the former traverses the internal 
Sinus superior 
Ampulla of external canal | 
Ampulla of superior canal | 
Macula acustiea utriculi | 
Raab & " | >) Superior semicircular canal 
Macula acustica sacculi 
Ramus vestibularis 
Nervus facialis | | 
Ramus cochlearis Ixternal semicircular canal 
Posterior semicircular canal 
Ligamentum 
spirale 
Membvana basilaris 
Branches of ramus Aaoanie of posterior canal 
cochlearis Beep oan 
Branch of ramus | Sinus inferior 
cochlearis to ampulla of posterior canal Ductns endolymphaticus 
Duetus reuniens 
Fic. 529.—MemMBRANOUS LABYRINTH of A FivE Montus’ Fastus, viewed from its postero-mesial 
aspect (Retzius). 
auditory meatus it presents a gangliform swelling, the ganglion of Scarpa. The ramus 
vestibularis divides into three branches, which are distributed to the macula 
acustica utriculi and the ampulle of the superior and external semicircular 
canals. The ramus coehlearis gives off a branch to the macula acustica sacculi 
and another to the ampulla of the posterior semicircular canal. The remainder of 
the ramus cochlearis is distributed to the hair cells of Corti’s organ, the branches for 
the basal and middle coils entering the foramina in the tractus spiralis foraminosus, 
those for the apical coil passing up through the canalis centralis of the modiolus. 
Extending upwards, in the bony canals of the modiolus, the nerve fibres radiate 
outwards between the lamell of the lamina spiralis ossea. Contained in the spiral 
canal of the modiolus, near the attached margin of the lamina,is a ganglion which 
winds spirally round the modiolus, and is named the ganglion spirale or ganglion of 
46 a 
