THE INTERNAL EAB 



697 



This elevation with its neuro-epithelial covering is known as the macula 

 acustica sacculi. 



The neuro-epithelium contains two varieties of cells, the sustentacu- 

 lar and the hair cells. The former, fiber cells of Eetzius, form a layer, 

 two or three cells deep, which rests upon the basement membrane, 

 and whose broad basal portion contains a spheroidal nucleus. Beyond 

 the nucleated portion the cytoplasm of the sustentacular cell is con- 



FIG. 582. TRANSECTION OF THE MARGIN OF THE MACULA ACUSTICA SACCULI OF A 

 GUINEA-PIG. 



a, otolithic membrane; b, hairs; c, cuticular membrane; d, hair cells; e, susten- 

 tacular cells; /, epithelium of the saccule; g, tunica propria; h, nerve fibers; i, bone. 

 Hematoxylin and eosin. X 325. (After Kolliker.) 



tinued inward between the bodies of the hair cells to the surface of 

 the epithelial layer, this portion of the cell being relatively slender. 



The hair cells occupy the superficial part of the epithelial layer 

 by their broad nucleated portions, which carry upon their free extremity 

 a single tuft of long stiff cilia, having the appearance of a delicate hair- 

 like process which projects into the endolymphatic cavity. That por- 

 tion of the endolymph which immediately overlies the macula, and 

 into which the hair-like processes project, though not essentially dif- 

 ferent in microscopic appearance in fresh tissues, appears to possess a 

 somewhat gelatinous consistence, and in it are suspended various forms 

 of minute crystals of calcium carbonate which are known as otoconia 

 or 'otoliths.' The free surface of the neuro-epithelium is also provided 

 44 



