818 



DISSECTION OF THE EAE. 





Tube 



divided 

 into two. 



Septum 

 bony and 

 membra- 

 nous. 



Osseous 

 part 



In the recent bone the tube is divided into two main passagef-l! 

 (scalse) by the septum (fig. 303). In the dry bone a remnant oi-Hi 

 this partition is seen in the form of a thin osseous plate /amirMMJ 

 spiralis, projecting from the axis. 



SEPTUM OF THE SPIRAL TUBE (fig. 304). The partition in the* 

 recent state dividing the tube of the cochlea into two passages,* 

 consists of an osseous and a membranous portion : 



The osseous part ( 3 ), formed by the lamina spiralis, extends about U 

 half-way across the tube. Inferiorly it begins in the vestibule, I 



FIG. 304. A DIAGRAM OF A SECTION OF THE TUBE OF THE COCHLKA, 



ENLARGED (MODIFIED FROM 



SV. Scala vestibult. 

 ST. Scala tympani. 

 CC. Canal of the cochlea. 



1. Membrane of Reissner. 



2. Cochlear branch of the auditory 

 nerve. 



3. Lamina spiralis ossea. 



4. Ligamentum spirale. 



a. Limbus laminae spiralis. 



b. Sulcus spiralis. 



c. Tympanic lip of the sulcus 

 spiralis. 



mb. Membrana basilaiis. 

 The remaining letters refer to 

 parts of the organ of Corti. 



ends above 

 in a point 



over an 

 aperture. 



Lamina 

 spiralis 



has limbus 

 on upper 

 surface. 



where it is wide, and is attached to the outer wall so as to shut out 

 the fenestra rotunda from that cavity ; and diminishing in size, it 

 ends above in a point the hamulus, opposite the last half-turn^of 

 the cochlea. Between the hamulus and the axis is a space, which 

 is converted by the membranous piece of the septum into a foramen 

 (hiatus, helicotrema; fig. 303, /), and allows the intercommunication 

 of the two chief passages of the cochlear tube. 



The lamina spiralis is formed by two plates of bone, which 

 enclose canals for vessels and nerves, and are separated farthest 

 from each other at the axis. The upper surface of the lamina is 

 covered in the outer fourth of its extent by a border or limbus of 



