THE ORGANS OF SENSE. 



By a second membrane a portion of the upper of these two canals is cut off from 

 the rest, constituting the scala media. The lamina spiralis ends above in a hook- 

 shaped process (hamuhts) -which partly bounds the helicotrema. At the point where 

 the osseous lamina is attached to the rnodiolus is a small canal, -which winds round 

 the modiolus, and was denominated by Rosenthal the canalis spiralis modioli ; it 

 is occupied by a swelling of the cochlear nerve, the ganglion spirale, in which 



FIG. 549. Longitudinal section of the cochlea, showing the relations of the scalae, the ganglion spirale, etc. 

 S. V. Scala vestibuli. S. T. Scala tympani. S. M. Scala media. L. S. Ligamentum spirale. G. S. Ganglion spi- 

 rale. 



ganglion-cells are found, and from which the nerves pass to the osseous lamina and 

 organ of Corti. The scala media belongs to the membranous labyrinth. 



The osseous lamina, as above stated, extends only part of the distance between 

 the modiolus and the outer bony wall of the cochlea. Near its outer end the 

 periosteum on the upper or vestibular surface of the lamina swells up into an 

 elevation which is called the limbus laminae spiralis (" denticulate lamina " of Todd 

 and Bowman). The lamina spiralis terminates in a grooved extremity, the sulcus 

 spiralis, which presents the form of the letter C : the upper part of the letter, 

 being formed by the overhanging extremity of the limbus, is named the labium 

 vestibulare ; the lower part, prolonged and tapering, is called the labium ty'mpani- 

 cum (Fig. 550). From the labium tympanicum a thin membrane extends over to 

 the bony wall of the cochlea, completing the scala tympani. This membrane is 

 called the membrana basilaris. At its outer attachment it swells out so as to form 

 a thick triangular structure, which was regarded as a muscle by Todd and Bowman 

 (cochlearis), but is now recognized as ligamentous the lie/amentum spirale. 

 Between the labium vestibulare and the attachment of the membrane of Reissner, 

 presently to be described, a very delicate membrane extends over to the outer 

 wall of the cochlea, running nearly parallel to the membrana basilaris. It was 

 described by Corti, and covers over the organ which is called after his name, and 

 is therefore called membrane of Corti, or membrana tectoria. Farther inward, 

 near the commencement of the limbus laminae spiralis, another delicate mem- 

 brane, the membrane of Reissner, is attached to the vestibular surface of the 

 periosteum of the osseous lamina and stretches across to the outer wall of the 

 cochlea. The canal which lies below the osseous lamina and membrana basilaris 

 is the scala tympani ; that which is bounded by the osseous lamina and membrane 

 of Reissner, the scala vcstibuli; while the space between the membrane of 

 Reissner and membrana basilaris is generally described as the Scala media, Can- 

 alis membranacea, or Canalis cochlea*, and this is the nomenclature which will be 

 used here. Others, however, apply the name canalis cochlea? only to the canal 



