210 STRUCTURE OF MACULA ACUSTICA. [Boon in. 



than hair cells), and that the nerve fibres, forming a plexus of 

 fibrillae in the lower layers of the epithelium, become connected 

 with the rod cells and not at all with the cylinder cells. According 

 to this view, the rod cells are the functional terminal organs and 

 the cylinder cells subsidiary structures. A third class of observers 

 maintain that both cylinder cells and rod cells bear hairs, that 

 both are connected with the fibres of the auditory nerve, and 

 that both serve as terminal organs. Probably however the view 

 which we first related is the more correct one, though the matter 

 cannot as yet be regarded as definitely settled. 



828. The maculae acusticse, both that of the utricle and 

 that of the saccule, resemble the cristse so far as essential features 

 of structure are concerned. In them as in the cristee both the 

 dermis and the epithelium are thickened, but the elevation thus 

 caused is in the form of a low swelling, not a steep ridge. The 

 epithelium, which bears auditory hairs, consists of cylinder cells 

 and rod cells, and the fibres of the auditory nerve enter into and 

 are lost among the cells in the same way as in the cristse. 

 Perhaps the most conspicuous difference is that in the maculae 

 the auditory hairs are distinctly shorter than in the cristse. 

 Above each macula lies a fibrinous mass, not unlike the cupula, 

 but having the form of a flat membrane ; it is stated however to 

 be a natural structure and not, like the cupula, an artificial product. 

 There are no essential differences in structure between the macula 

 of the utricle and that of the saccule. So far as we may permit 

 ourselves to draw from structural features inferences concerning 

 function, we may conclude that both the semicircular canals and 

 the utricle with the saccule perform very much the same func- 

 tions ; there is, so far as structure is concerned, nothing to 

 indicate that the afferent impulses started in the cristaa differ 

 from those started in the maculae. 



829. The endolymph, which we may look upon as secreted 

 by the epithelium lining the membranous labyrinth and so far 

 differing in origin from perilymph, resembles nevertheless that 

 fluid very closely, containing however rather less solid matter. 

 It is to a certain extent viscid, apparently owing to the presence 

 of mucin. 



In both the utricle and saccule are suspended in the endo- 

 lymph crystalline bodies composed of calcium carbonate, with 

 traces of other salts and with 25 p.c. or less of organic matter. 

 In man and the higher animals, though varying in size, they are 

 small crystals, generally rhombic or octohedral ; and are then 

 generally called otoconia. In some of the lower animals, for 

 instance fishes, they form large masses, and are then generally 

 called otoliths. The otoliths, and for the most part the otoconia, 

 are confined to the utricle and saccule, and are usually found 

 imbedded in the membrane spoken of above, which is hence some- 

 times called the " otolith " or " otoconial membrane." Otoconia 



