840 



A MANUAL OF PHYSIOLOGY 



The internal ear consists of the bony labyrinth, a series of curiously 

 excavated and communicating spaces in the substance of the petrous 

 portion of the temporal bone, filled with a liquid called the peri- 

 lymph, in which, anchored by strands of connective tissue, floats a 

 corresponding series of membranous canals (the membranous laby- 

 rinth), filled with a liquid called endolymph. The labyrinth of the 

 internal ear is divided into three well-marked parts : the cochlea, the 

 vestibule, and the semicircular canals (Fig. 324). The cochlea, the 

 most anterior of the three, consists of a convoluted tube which coils 

 round a central pillar or modiolus like a spiral staircase. The 

 lamina spiralis projects from the modiolus and divides the tube into 

 an upper compartment, the scala vestibuli, and a lower, the scala 



r. 



mb 



FIG. 326. ORGAN OF CORTI < BARKER, AFTER RETZIUS). 



mb, basilar membrane ; tb, its tympanal covering ; vs, blood-vessel (vas spirale) ; 

 re, medullated distal processes of bipolar nerve-cells in the ganglion spirale passing 

 in to arborize around the hair-cells ; is, epithelial cells continuous with the epithelium 

 of the sulcus spiralis internus ; /, inner pillar of Corti, with its basal cell b ; p' outer 

 pillar with us basal cell V; i, 2, 3 supporting cells of Deiters, whose processes run up 

 to DC attached to the lamina reticularis, r; H, Hensen's supporting cells C cells of 

 Claudius ; i internal hair-cell with its hairs, i' (the upper part of the hair-cell is con- 

 cealed by the head of the inner pillar of Corti) ; e, external hair-cell ; ', hairs of three 

 jrnal hair-cells ; n, n* to 4 , cross-sections of the spiral strand of cochlear nerve-fibres. 



tympani (Fig. 325). The part of the lamina next the modiolus is 

 of bone, but it is completed at its outer edge by a membrane, the 

 lamina spiralis membranacea. The scala tympani abuts on the 

 fenestra rotunda, and its perilymph is only separated from the air of 

 the tympanic cavity by the membrane which closes that opening. 

 At the apex of the cochlea the lamina spiralis is incomplete, ending 

 in a crescentic border, so that the scala tympani and the scala 

 vestibuli here communicate by a small opening, the helicotrema. 

 The scala vestibuli communicates with the vestibule, and the vesti- 

 bule with the semicircular canals, so that the perilymph of the entire 

 labyrinth forms a continuous sheet, separated from the cavity of the 

 middle ear by the structures that fill up the round and oval foramina 



