198 



INTRODUCTION TO NEUROLOGY 



sensory epithelium, part of whose cells are supporting elements of diverse 

 sorts and part (the hair cells) are specific receptors. The termini of the 

 cochlear nerve arborize around the bodies of the hair cells in the same way 

 that fibers of the vestibular nerve are related to the hair cells of the cristaj 

 of the semicircular canals (Fig. 32, p. 88). The membrana tectoria is 

 a delicate gelatinous mass resting upon the spiral organ and intimately 

 connected with the hairs of the hair cells. Its shape has been very care- 

 fully studied by Hardesty. 



Many details of the structure of the spiral organ, or organ of Corti, and 

 the whole question of the mode of its functioning are still controverted. 

 Our present knowledge of the histqlogical organization of the basilar mem- 

 brane shows that it is structurally incapable of serving the function of tone 

 analysis in the way postulated by Helmholtz's theory. Based upon im- 

 portant additions to our knowledge of the minute structure of the organ 



Fig. 94. Section through the apical turn of the cochlea of the pig at 

 about full term, showing outer auditory hairs embedded in the membrana 

 tectoria: ep.s.sp., Epithelium of spiral sulcus; i.h.c., inner hair cells; i.pil., 

 inner pillar; m.bas., basement membrane; m.tect., membrana tectoria; lab. 

 vest., labium vestibulare; n.coch., cochlear nerve; o.h.c., outer hair cell; s.sp., 

 sulcus spiralis. (After C. W. Prentiss.) 



of Corti and clinical observations upon diseased conditions, several different 

 theories of the mechanism of tone analysis have recently been expressed. 

 Among the more important of these researches are those of Shambaugh. 

 This author has demonstrated that the hairs of the hair cells do not termi- 

 nate freely in the endolymph, as commonly figured, but that they are 

 firmly attached to the under surface of the tectorial membrane. This 

 membrane has a semigelatinous texture and is capable of taking up sym- 

 pathetically the vibrations of the endolymph within which it floats. 



The development of the tectorial membrane has recently been restudied by 

 Prentiss and Hardesty. It first appears as a thin cuticular plate developed 

 over the free ends of the columnar cells which form the inner or axial part of 

 the epithelium of the basement membrane. In the adult ear it retains its 

 attachment to the labium vestibulare along the axial border of the ductus 

 cochlearis, but becomes free from the cells which form the lining of the 



