374 



AX .\Mi:ni(AX TEXT-HOOK OF PHYSIOLOGY. 



Pig. 192.— Diagram showing the epithelial cellsof 

 a macula or a crista (after Foster): 1, cylinder or 

 hair-cell ; 2, the same, enveloped in a nest of nerve- 

 fibrils; 3, 4, 5, forms of rod- or spindle-culls. 



shape and reaching only pan way to the basement membrane, the hair-cells; 

 the other, aarrow and elongated, the supporting or mxientaeular cells. The 

 former are peculiar in the fact that from their free ends there project long, 

 -till*, hair-like processes. The filaments of the ampullary-nerve branches 

 puss through the crista and encircle the bodies of the hair-cells. The cells 



/covering the maculae acustica have 

 / essentially the same structure as those 



just described, though in the maculae 

 the auditory hair- are shorter than in 

 the eristic. Seated on the free surface 

 of the macular epithelium is a fibrous 

 mass which is said to be a normal 

 structure, and not, like a somewhat 

 similar mass found covering the crista' 

 in post-mortem section, a coagulum 

 due to the method of preparation. 

 Imbedded in the membrane over the 

 maculae of both saccule and utricle 

 are small crystals, otoliths or oto- 

 conia, composed chiefly of carbonate 

 of lime. Otoconia are also found 

 less constantly in the ampullae and 

 even in the perilymph space of the cochlea. In fishes there are large masses 

 of calcareous matter, otoliths, attached to the wall of the auditory sac. 



General Anatomy of the Cochlea. — By far the most complex structure of 

 the ear is found in the cochlea (PI. 1. Figs. 1, 3, 4 ; Figs. 188-191). The bony 

 cochlea continues from the anterior wall of the vestibule, and in the upright posi- 

 tion of the head the axis of the modiolus is nearly horizontal, pointing, from base 

 to apex, outward and slightly down and forward, the base of the cochlea being 

 formed by the inner surface of the petrous bone. The membranous cochlea, 

 canalis or ductus cochlearis, is a tube of nearly triangular cross-section which 

 winds round the modiolus from base to apex | Fig. 193). The base or outer side 

 of this triangle is attached closely to the bony wall of the cochlea; the upper 

 side, supposing the modiolus to be vertical with its apex above, is made of a thin 

 sheet of cells known as the membrane of Reissner ; the lower side is made up 

 partlv of the bony margin of the lamina spiralis and partly of a membrane, 

 radially striated, stretched across from the edge of the spiral lamina to the side 

 wall of the cochlea; this i- called the basilar membrane, iii<ni!>r<tii<t hasilaris. 

 The coiled tube forming the bony cochlea is thus divided by the lamina spiralis 

 and the <-<ni<ifis cochlearis into three tubes which wind spirally and parallel 

 round the modiolus. The canalis cochlearis contain- endolymph, and its cav- 

 itv ends blindly above and below, but is continuous by way of the narrow 

 canalis reuniens with that of the saccule. The tubes above and below the 

 canalis cochlearis are perilymph-spaces ; it will be noticed that there is no 

 such space on the outer side of the membranous cochlea. 



