EAR 471 



ment cells. This is followed by a narrow basement membrane said to 

 form small nodular elevations toward the third and innermost layer, the 

 simple flat epithelium. Near the maculae and cristae the connective tissue 

 and the basement membrane become thicker, and the epithelial cells are 

 columnar with a cuticular border. In the neuro-epithelium of these 

 areas there are two sorts of cells, sustentacular and hair cells. The sus- 

 tentacular or fiber cells extend clear across the epithelium and are some- 

 what expanded at both ends ; they contain oval nuclei. Hair cells, which 

 receive the stimuli, are columnar cells limited to the superficial half of the 

 epithelium; they have large spherical nuclei near their rounded basal ends, 

 and a clump of fine agglutinated filaments projecting from their free sur- 

 face. The nerves lose their myelin as they enter the epi- 

 thelium and ascend to the bases of the hair cells. There ** 



they bend laterally, forming a dense network which ^ 



appears as a granular layer in ordinary preparations; ^ ^ 



the granules are optical sections and varicosities. ^ 



The horizontal fibers terminate like their occasional FIG. 476. OTOCONIA 

 branches, by ascending between the hair cells, on the LUSOF T AN INFANT" 

 sides of which they form pointed free endings. They 

 do not reach the free surface of the epithelium. This surface is covered by 

 a continuation of the cuticula, a "membrana limitans," which is perforated 

 by the hairs. Over the two maculae there is a soft substance containing 

 very many crystals of calcium carbonate, 1-15 /* long, which are named 

 otoconia. (Large "ear stones" of fishes are called otoliths.) Over the 

 cristae of the semicircular ducts there is a gelatinous substance, transparent 

 in fresh preparations, but coagulated and rendered visible by reagents. 



The "ligaments" of the ducts, the thin periosteum of the bony semi- 

 circular canals, and the perilymph spaces lined with mesenchymal epithe- 

 lium are seen in Fig. 473. 



COCHLEA. 



The relation between the ductus cochleae and the scalae tympani and 

 vestibuli is shown in Fig. 474. The ductus is triangular in cross section, 

 being bounded on its peripheral surface by the thick periosteum of the 

 bony wall of the cochlea; on its apical surface (toward the cupola) by the 

 membrana vestibularis (Reissner's membrane) ; and on its basal or medial 

 surface by the lamina spiralis. These three walls may be described in 

 turn. 



The peripheral wall of the cochlear duct is formed by the dense fibrous 

 periosteum attached to the bone, together with a large mass of looser 

 tissue crescentic in cross section, the ligamentum spirale (Fig. 477). The 

 spiral ligament is covered by a layer of cuboidal epithelial cells belonging 



