610 THE NERVOUS SYSTEM. 



them to the corresponding wall of the osseous labyrinth. In these 

 bands are the blood-vessels and the fibers of the auditory nerve 

 which are distributed to the utricle, saccule, and membranous 

 semicircular canals. 



Utricle. The utricle or utriculus is situated in the upper and back 

 part of the vestibule at the fovea hemi-elliptica, and is oblong in 

 shape. It communicates posteriorly with the membranous semi- 

 circular canals by five openings, and from it passes a small canal 

 which unites with one from the saccule, the two forming the ductus 

 endolymphaticus. Branches of the auditory nerve pierce the wall 

 of the utricle at one point, and here the tunica propria is thick- 

 ened, and the epithelium consists of columnar cells upon which 

 are long, stiff", tapering hairs, around which the axis-cylinders 

 of the auditory nerve-fibers ramify. Schafer, to Whom we are 

 indebted for this description, says that these are like the rod- 

 and cone-elements of the retina, the bipolar cells of the olfactory 

 membrane, and the gustatory cells of the taste-buds sensory or 

 nerve-epithelium cells. Between the hairs are nucleated cells, 



FIG. 389. Section of macula of utricle, human : n. utr., bundles of the utricular 

 branch of the eighth nerve; h, auditory hairs; p.l.s., perilymphatic space (G. 

 Betzius). 



fiber-cells of Retzius, which rest upon the basement-membrane, 

 and are connected at their free extremity with a cuticular mem- 

 brane through which the auditory hairs project. The auditory 

 hairs do not project free into the endolymph, but into a soft, 

 mucus-like substance of a dome-like form in the ampullae, and 

 which in the saccule and utricle has a mass of calcareous particles, 

 otoliths, embedded in it. The otoliths are also called otoconia and 

 ear-stones, and are minute crystals of calcium carbonate. The 

 thickening of the tunica propria with the modified cells, etc., just 

 described, forms the macula acustica in the utricle and saccule 

 (Figs. 389, 390). In the ampullae of the semicircular canals the 

 columnar cells and auditory hairs are upon a ridge, and here 

 the structure is called crista acustica. The cristse of the ampullae 

 have essentially the same structure as the maculae of the utricle 

 and saccule, save that the otoliths are absent. 



Saccule. The saccule or sacculus is globular, smaller than the 

 utricle, being about 3 mm. by 2 mm. in diameter, and lies in the 

 fovea hemispherica. It receives nervous filaments derived from 



