THE MEMBRANOUS COCHLEA. 



115 



The floor itself of the cochlear canal is formed of a narrow portion of the spiral 

 lamina external to the membrane of Reissner, and of the basilar membrane. In the 

 macerated specimen this part of the lamina thins off gradually to a fine edge like the 

 blade cf a knife, but in the recent condition (fig. 129) it retains its thickness for 

 some distance (or even exhibits a slight increase), and then abruptly terminates with 

 a border which in section is C-shaped, with the lower limb of the C (labium 

 tympanicwri) much more prolonged and tapering than the upper (labium vesti- 

 bulare). The lower limb is in fact the section of the end of the osseous lamina, 

 together with a thin membranous 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. 131, l\ with its somewhat 



s.v 



Fig. 131. SECTION ACROSS THE BASAL TURN OP THE HUMAN COCHLEA. (G-. Retzius.) Magnified. 



D.C, ductus cochleae ; s.v, scala vestibuli ; s.t, scala tympani ; II, membrana Reissneri ; Mt, mem- 

 brana tectoria ; b.m, membrana basilaris ; str.v, stria vascularis ; l.sp, ligamentum spirale ; 1, limbus ; 

 s.sp, sulcus spiralis ; t. C, tunnel of Corti ; n, nerve fibres ; sp.l, spiral lamina. 



overhanging, crest-like edge, is known as the limbus 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 groove (fig. 131, s.sp.). 



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

 nective tissue. Towards the under and inner part there are numerous corpuscles, and 

 the texture is fibrous, but above and near the crest few or no connective tissue cor- 

 puscles are met with, but the tissue has a columnar aspect with somewhat regularly- 

 arranged nuclei. The fibrillated tissue is prolonged, as just intimated, beyond the 

 osseous lamina, into the basilar membrane. Near its termination, close to the 

 junction with the basilar membrane, it is perforated with a number of regularly- 

 arranged, elongated apertures (fig. 132,^?), about 4,000 in number, which serve for 

 the transmission of bundles of the nerve-fibres. The latter, in their course from 

 the spiral ganglion to the auditory epithelium, are lodged, as far as this, in canals in 

 the lower osseous part of the spiral lamina. Their arrangement will be afterwards 

 more fully described. 



i 2 



