474 HISTOLOGY 



shortest in the basal part of the cochlea and longest toward the apex, 

 corresponding in length with the basal layer of the cochlear duct. These 

 fibers have been thought to vibrate and assist in conveying sound waves 

 to the nerves, but theories which assume that the basilar membrane is 

 a "vibrating mechanism" are considered untenable by Hardesty; he finds 

 it more probable that the membrana tectoria vibrates and transmits 

 stimuli to the neuro-epithelium. 



The epithelial cells covering the basilar layer occur in rows of highly 

 modified forms, which extend up and down the cochlear. duct, constituting 

 the spiral organ (organ of Corti). Next to the cuboidal epithelium of 

 the sulcus spiralis there is a single row of inner hair cells 

 (Fig. 480). These are short columnar cells which do 

 not reach the bottom of the epithelium; each has about 

 forty long stiff hairs on its free surface. The inner 

 hair cells are followed peripherally by two rows of 

 pillar cells, the inner and outer, which extend the whole 

 length of the cochlear duct. As seen in cross section 

 F IG . 479. SURFACE they are in contact above, but are separated below by 



VIEW OF THE . . , ., , . - . 



LAMINA SPIRALIS a triangular intercellular space or tunnel, which is 



MEMBRANACEA OF ..... 



A CAT. x 240. filled with soft intercellular substance. Thus they rest 



Drawn with 



change of focus. upon the basilar membrane in A -form. Each pillar 



e, Epithelium ( cells of r ,,..,,. 11 , j , 



Claudius) of the cell may be subdivided into a head, a slender body, 



ductus cochleans J 



o" thTmembrana an ^ an ex P an< ied triangular bas'e. The greater portion 



bf s nuc?ei n of oc the ^ eac ^ ce ^ nas been transformed into a resistant band, 



nec d t!ve y t^ue con " at the base of which, within the tunnel, there is a mass 



of protoplasm containing the nucleus. A protoplasmic 



sheath extends up from the base around the body of the cell. Dark round 



structures which may be found in the heads of the pillars, and at the 



foot of the outer ones, are not nuclei, but are "probably of horny nature." 



The heads of the pillars interlock. Both pillars produce "head-plates" 



directed outward, and so arranged that the plate from the inner pillar 



overlies that from the outer pillar (Fig. 480). Moreover, the round head 



of the outer pillar is fitted into a concavity in the head of the inner pillar, 



as shown in the figure. 



On the peripheral side of the outer pillars there are several rows 

 (usually four) of outer hair cells separated from one another by sustenlacu- 

 lar cells (Deiter's cells). The outer hair cells have shorter hairs than the 

 inner ones, and are characterized by the presence of "Hensen's spiral 

 bodies," one of which occurs in the outer half of each cell. These bodies, 

 shown as dark spots in Fig. 480, probably represent a trophospongium. 

 The centrosomes of the hair cells are always in their upper ends. Like 

 the inner hair cells, the outer ones do not extend to the basilar membrane, 

 thus leaving unoccupied the communicating intercellular spaces between 



