850 



THE OKGANS OF SENSE. 



of the cochlear nerves, and is continuous with the membrana basilaris. The upper 

 surface of the labium vestibulare presents a number of furrows crossing each other 

 nearly at right angles, and intersecting a series of elevations which, at the free 

 margin of the labium, form a row of tooth-like structures, about 7000 in number, 

 the auditory teeth of Huschke. Covering the limbus is a layer of apparently 

 squamous epithelium ; the deeper protoplasmic portions of the cells, however, with 

 their contained nuclei, lie in the intervals between the elevations and auditory 

 teeth. This layer of epithelium is continuous above with that covering the under 

 surface of the membrana vestibularis and below with that which lines the sulcus 

 spiralis internus. 



Membrana Basilaris. The inner part of this membrane is thin, and supports 

 the organon spirale ; it is named the zona arcuata, and reaches as far as the foot- 

 plate of the outer rod of Corti. Its outer part, extending from the foot-plate of 

 the outer rod of Corti to the crista basilaris, is thicker and distinctly striated, 

 and is termed the zona pectinata. The substantia propria of the membrane is 

 almost homogeneous, but exhibits, in its deeper part, numerous fibres. These fibres 

 are most distinct in the zona pectinata, and number, according to Ketzius, about 

 24,000. Covering the under surface of the membrana basilaris is a layer of con- 

 nective tissue, containing, in its inner part, small blood-vessels ; one of these is 

 larger than the others and lies below the tunnel of Corti, and is named the vas 

 spirale. The width of the membrana basilaris increases from 210 //, in the basal 

 coil to 360 //. in the apical coil. 



Organon Spirale (O.T. Organ of Corti) (Fig. 725). Placed upon the inner 

 portion of the membrana basilaris, the organon spirale consists of an epithelial eminence 

 which extends along the entire length of the ductus cochlearis, and comprises the 

 following structures, viz. : (1) Corti's rods or pillars, (2) hair cells (inner and outer), 

 (3) supporting cells of Deiters, (4) the cells of Hensen and Claudius, (5) the lamina 

 retieularis, and (6) the membrana tectoria. 



The rods of Corti form two rows, inner and outer, of stiff, pillar-like structures, and 

 each rod presents a base or foot-plate, an intermediate elongated portion, and an upper 



Outer rod of Corti 



Inner rod of Corti 



Inner hair cell 

 Hensen's stripe 



Membrana tectoria 

 Sulcus spiralis 

 Limbus laminaj internus 

 spiralis 



Outer hair cells 



Cells of Hensen 



Membrana basilaris 



Cells of Claudius 



*&&#* ^ 



Cells of Deiters 



Vas spirale Space of Nuel 



Tunnel of Corti 



FIG. 725. TRANSVERSE SECTION OF THE ORGANON SPIRALE FROM THE CENTRAL COIL 



OF THE DUCTUS COCHLEARIS (Ketzius). 



end or head. The bases of the two rows are planted on the membrana basilaris son: 

 little distance apart. The intermediate portions of the rods incline towards each oth( 

 and the heads come into contact, so that, between the two rows above and the membraii 

 basilaris below, a triangular tunnel, the tunnel of Corti, is enclosed ; this tunnel increas< 

 both in height and width on passing towards the apex of the cochlea. The inner roc 

 number nearly 6000, and the head of each resembles somewhat the proximal end of tl 

 ulna, presenting externally a deep concavity for the reception of a corresponding coi 

 vexity on the head of the outer rod. The part of the head which overhangs this concavil 

 is prolonged outwards, under the name of the head-plate, and overlaps the head of tl 



