STRUCTURE OF THE LABYRINTH. 



281 



the cristse of the ampullae, and along the whole length of the canal of 

 the cochlea (the shaded parts in fig. 312). 



At these places the lining epithelium is specially modified to form 

 a, sensory or nerve-epithelium; elsewhere it is a simple pavement- 

 epithelium. 



s.s.c. 



s.e. 



FIG. 312. PLAN OF THE RIGHT MEM- 

 BRANOUS LABYRINTH VIEWED FROM 

 THE MESIAL ASPECT. 2 



r 



u, utricle, with its macula and the three 

 semicircular canals with their ampullae ; 

 s, saccule ; aq.v., aquseductus vestibuli; 

 s.e., saccus endolymphaticus ; c.r., canalis 

 reunions ; c.c. canal of the cochlea. 



FIG. 313. VIEW OF THE INTERIOR OF 

 THE LEFT OSSEOUS LABYRINTH. 



The bony wall of the labyrinth is removed 

 superiorly and externally. 1, fovea hemi- 

 elliptica ; 2, fovea hemisphajrica ; 3, com- 

 mon opening of the superior and posterior 

 semicircular canals ; 4, opening of the 

 aqueduct of the vestibule ; 5, the superior, 

 6, the posterior, and 7, the external semi- 

 circular canals ; 8, spiral tube of the coch- 

 lea ; 9, scala tympani ; 10, scala vestibuli. 



The -membranous semicircular canals and the utricle and saccule 

 are composed of fibrous tissue, which is adherent along one side to the 

 endosteum of the bony canal ; from the opposite side bands of fibrous 

 tissue pass across the perilymph. Within the fibrous membrane is a 

 thick clear tunica propria, which, in the semicircular canals, forms 

 papillary elevations in the interior of the tube (figs. 314, 315). 



The places of entrance of the nerve-fibres into the ampullae are 

 marked by a transverse, inwardly projecting ridge (crista), in the 

 saccule and utricle by a thickening of the tunica propria (macula). 

 The epithelium at these places is formed of columnar cells (fig. 316), 

 which are surmounted by long, stiff, tapering hairs (auditory hairs, 

 fig. 316, h), and to these hair-cells the axis-cylinders of the nerve-fibres 

 pass directly (fig. 317); they are therefore 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 them are a number of thin and somewhat rigid nucleated 

 cells (fibre-cells of Retzius, fig. 317, /), which rest upon the basement- 

 membrane, and are connected at their free extremity with a cuticular 

 membrane, through which the auditory hairs project. 



