CHAP, iv.] 



HEARING. 



213 



the basilar membrane (Figs. 177, 179 m.b.~). It may be regarded 

 as consisting of two parts, one reaching radially from the tympanic 

 lip to a point marked by the attachment of what we shall pre- 

 sently speak of as the feet of the outer rods of Corti, the other 

 continued on from this point to the spiral ligament. In its first 

 more median part the basilar membrane is a thin rigid sheet 

 which, though distinctly fibrillated radially, cannot be said to be 

 composed of definite fibres. In its second, more lateral part, the 

 membrane becomes somewhat thicker, thinning however again as 

 it approaches the spiral ligament, and is obviously composed 

 of fibres, lying side by side and cemented by or imbedded in a 

 homogeneous ground-substance differing in nature from the fibres 

 themselves. The fibres, when isolated are stiff, bending at a sharp 

 angle, not curling, and are easily broken. 



On its tympanic side, the basilar membrane bears, resting 

 on a thin layer of homogeneous ground substance, a lymphatic 

 epithelium (Figs. 177, 179 t.L), the cells of which, often more 



tv 



naud 



mb 



g-sp 



FIG. 179. DIAGRAM OF THE ORGAN OF CORTI. (After Retzius ) 

 i.r. inner rod of Corti, o.r. outer rod of Corti. 



i.k.c. inner hair-cells, n.c. the group of nuclei beneath it. o.h.c. outer hair-cell, or 

 cell of Corti, of the first row, c.D. its twin cell of Deiters ; four rows of these 

 twin cells are shewn. 



n.aud. the auditory nerve perforating the tympanic lip l.t, and lost to view among 

 the nuclei beneath the inner hair-cell, i.sp.n. the inner spiral strand of nerve- 

 fibrilhB. t.sp.n. the spiral strand of the tunnel, o.sp.n. the outer spiral 

 strand belonging to the first row of outer hair-cells ; the three succeeding 

 spiral strands belonging to the three other rows are also shewn. Nerve 

 fibrillae are shewn stretching radially across the tunnel. 



H.c. Hensen's cells, Cl.c. Claudius cells, m.b. basilar membrane, tl. lymphatic 

 epithelioid lining of the basilar membrane on the side towards the scala 

 tympaui. Ig. sp. spiral ligament, c'. cells lining the spiral groove, overhung 

 by t.v. the vestibular lip. m.t. the tectorial membrane ; a fragment of it is 

 seen torn from the rest and adherent to the organ of Corti just outside the 

 outermost row of outer hair-cells. 



than one layer deep, are spindle shaped, the cell substance being 

 prolonged into filamentous processes taking a longitudinal, that 

 is to say spiral, direction along the length of the canal. Near 



