THE EAR. 



409 



Fig. 310. 



externa, so that between the two a tolerably 

 deep sulcus, semicanalis spiralis (Huschke), 

 opening externally, is left. Towards the 

 axis of the cochlea the so-termed " teeth" 

 are directly continuous, with similarly con- 

 stituted, elongated ridges or cost a (fig. 

 309 a a), which are occasionally conjoined 

 in pairs, or divided into two, and still 

 further inwards break up into divisions, 

 which become shorter and shorter and 

 smaller and smaller, being at first elongated 

 and afterwards rounded. In the longitu- 

 dinal and transverse grooves between these 

 costce and tubercles and the teeth, there 

 usually exists, in single series, rounded or 

 elongated, opaque glistening corpuscles (e), 

 0*0015— 0-002— 0-003'" in size, which, on 

 the addition of acetic acid, prove to be 

 nuclei; and by the same reagent, nuclei- 

 form stria occasionally become distinct in 

 the pale and somewhat swollen "teeth" 

 and costce, which parts, consequently, as 

 well as those presently to be described, I 

 am inclined to regard as belonging to the 

 connective-tissue group. 



The habenula externa s. denticulata (h-t) 

 arises under the base of the a teeth" of the 

 first series, directly from the just-described 

 habenula sulcata, and constitutes at first 

 the bottom of the spiral sulcus noticed 

 above. In most places its thickness does 

 not amount to more than 0-001"', which is also that of 



Fig. 310. Vestibular surface of the lamina spiralis membranacea, x 225 diam. 

 The letters are in part the same as in fig. 309 : a a, cylindrical elevations of the 

 habenula sulcata : 6, spot where a " tooth of the first series" originates ; y, spaces 

 between the " apparent teeth ;" $, anterior portion of a " tooth of the second series" 

 thrown back ; e, the same in its natural position, without its epithelial cells ; £, the 

 same with only the lowermost epithelial cells ; »/, the same with two of the lower- 

 most cells ; $, streaks or slight elevations of the zona pectinata ; k, periosteum, by 

 which the lamina spiralis is attached, with spaces, X, between the bundles. After 

 Corti. 



