THE MEMBRAXOUS LABYRINTH. 



649 



Fig. 463. 



The tunica pi'opria k a clear, glassy, membranous structure continuous 

 around the whole tube, although thinning off very much opposite the part 

 where the membranous canal is in contact with the bone (fig. 462, 5). 

 Externally it is not very distinctly marked off from the fibrous coat : 

 internally it presents not a smooth surface but a number of paj^illiform 

 eminences (fig. 4G2, 3, 6), which project into the interior of the canal 

 except at the thinnest part. According to 

 Riidinger, these eminences are found almost 

 constantly in the adult. 



The epitlielial hning is continuous, both 

 over and between the papilliform projec- 

 tions. In the human semicircular canals 

 the cells are of the same nature and form 

 throughout, but in many of the lower 

 animals — birds and fish — a part takes on 

 somewhat of a columnar character, while 

 in one species of fish, (Salmo hucho), as 

 described ])y Riidinger, a tract of cells 

 along the whole length of each canal be- 

 comes remarkably developed into two rows 

 of heaped-up, rounded cell-bodies, from 

 each of which a long filament extends to 

 the wall of the canal in a direction trans- 

 verse to the axis. 



The meaning of these modifications of structure 

 is unknown. No nerves have hitherto been 

 seen proceeding to the parts in question ; but they 

 apparently re^jresent the much more developed 

 peculiarly modified epithelium •which, as we shall 

 immediately see. is found in the ampulla3 and in 

 the saccule and utricle ojiposite the parts where 

 the corresponding branches of the auditory neiwe 

 enter, and which receives the ultimate termina- 

 tions of those nerves. 



The ampulla?, as well as the saccule 

 and utricle, agi-ee generally in structure 

 with the semicircular canals : at the part, 

 however, where they are connected to the 

 osseous wall the fibrous outer layer forms a 

 loose-meshed tissue, and the tunica propria 

 is very much thickened, and in the am- 

 pullae causes a rounded transverse projec- 

 tion into the cavity of each, the sejifum 

 transversum, or crUta aci(i<ticc(, before . men- 

 tioned. Over this projection, and also to a 

 certain extent in its neighbourhood, the 

 epithelium is of an elongated columnar 

 form (fig. 4G3, c), and is surmounted by 

 long and fine cilium-like processes (auditory hairs (A) ), which are, 

 however, not spontaneously vibratile, but project stiffly into the endo- 

 lymph. These hairlets are said to belong not to the columnar epithelium, 

 cells themselves, but to spindle-shaped cells (s;;), which he between 





Fig. 463. — Diagram of ths 

 Auditory Epithelium ani> 

 THE Mode of Termination 

 OP THE Nerves op thk 

 Ampulla (afterM. Schultze). 



c, columnar epithelinm ; sp, 

 spindle-shaped cells, each .sup- 

 porting an auditory hair, h; 6, 

 basal supporting cells ; n, two 

 nerve fibres passing through the 

 tunica propria to join the plexus 

 in the epithelium ; I, limit of 

 tunica propria. 



