THE MEMBRANOUS LABYRIXTK. 



653 



Fiff. 4GS. 



spiral lamina in front of the floor of the vestibule. Xear to this blind 

 extremity the eanalis membranaceus receives a small canal, lined with 

 epithelium, eanalis retniims (Hensen), which is continued from the 

 saccule of the vestibule like the neck of a flask, and enters the canal 

 of the cochlea abruptly nearly at a right angle (fig. 4G8, cr). The 

 cavity of the eanalis membranaceus is thus rendered continuous with 

 that of the saccule. 



It is the structures which are found upon the flooi' of this spirally- 

 wound triangular canal of the cochlea that claim more particular 

 attention, for it is to them that the branches of the cochlear 

 nerve are distributed, and upon them the fanetion of the cochlea 

 as a part of the auditory apparatus appears more especially de- 

 pendent. 



The floor itself of the coch- 

 lear canal is formed of a narrow 

 portion of the spiral lamina 

 external to the membrane of 

 Eeissner, and of the basilar 

 membrane. In the macerated 

 specimen this part of the lamina 

 thins off gradually to a fine edge 

 like the blade of a knife, but in 

 the recent condition(fig.4G7, Us) 

 it retains its thickness for some 

 distance (or even exhibits a 

 slight increase), and then ab- 

 ruptly terminates with a border 

 which in section is C-shaped 

 with the lower limb of the C 

 much more prolonged and taper- 

 ing than the upper. This lower 

 -imb is in fact the section of 

 the end of the osseous lamina, 

 together with a thin mem- 

 branous layer which covers it, 

 and which is directly prolonged 

 into the basilar membrane. This 

 membrane, as well as the whole 

 thickened upper part of the edge 

 of the spiral lamina, not being 

 ossified, disappears in the process 

 of maceration. The thickened 

 part (fig. 467, Us), with its somewhat overhanging, crest-like end (fig. 

 469, Or), is known as the Umhus of the spiral lamina, and the groove 

 which it overhangs, and which in section is represented by the bay of 

 the C, is known as the spiral r/roore (fig. 467, ss, fig. 460, S. sp. i). 



The tissue of which the limbus is composed seems to be a form of 

 connective tissue ; but it differs in diflPerent parts. Towards the under 

 and inner part there are in particular numerous. corpuscles, and the 

 texture is distinctly fibrous, but above there are few or no corpuscles, 

 and the tissue is more homogeneous ; although a feint fibrillation in a 

 radial direction, i.e., from within outwards, may still be traced in it. 

 This faintly fibrillated tissue is prolonged, as just intimated, beyond 



Fig. 468. — The Left Labykinth of a Child 

 AT Birth, partially opened on its outer 

 side to show the coilmencement of the 

 Membranous Canal of the Cochlea 

 (slightly altered after Eeicliert). f 



The external or horizontal canal has been 

 removed ; c s, supei'ior canal ; c j), posterior 

 canal ; a s, membranous ampulla and tube of 

 the superior canal cut short ; ah, that of the 

 external or hoi'izontal canal ; li, undilatedend 

 of the horizontal canal in front of the common 

 opening of the superior and posterior canals ; 

 p s, united superior and posterior canals ; u, 

 utriculus ; s, sacculus ; c c, vestibular part or 

 commencement of the membranous canal of 

 the cochlea ; c r, eanalis reunions connecting 

 it with the sacculus ; c, cochlea. 



