HISTOLOGY OF NERVE TISSUES 65 
diagram from the slide showing the location of the various layers and 
any details which you can see clearly. 
The Spiral Organ of Corti 1 (slides showing sections through the 
cochlea of the ear of the pig are recommended).—Locate in the 
section a transverse section through a turn of the cochlea. Study 
this under low power and note the rounded form of the bony tube; 
the triangular form of the section through the ductus cochlearis, 
in which the spiral organ of Corti lies supported on the lamina 
basilaris (basilar layer) which stretches between the bony shelf 
(the lamina spiralis ossea) and the opposite wall of the tube; the 
scala vestibuli, separated from the ductus cochlearis by a delicate 
membrane usually torn in the sections (the membrana vesti¬ 
bularis Reissneri); the scala tympani, separated from the ductus 
cochlearis by the lamina basilaris; the membrana tectoria, sup¬ 
ported from the lamina spiralis ossea and overhanging the spiral 
organ; the spiral ganglion of the cochlea, lying in the lamina 
spiralis and sending nerve bundles beneath the lamina spiralis to 
reach the spiral organ of Corti. 
Under the high power study the details of the spiral organ of 
Corti. Note within this, the rounded triangular section of a cavity 
which accompanies the spiral organ through the windings of the 
cochlea, and is known as the tunnel. The base of this rests 
on the lamina basilaris, and the two sides are formed by the rods of 
Corti. The larger portion of the spiral organ of Corti lies on the 
outer side of the tunnel and consists of numerous tall epithelial 
cells specialized from the general epithelial lining of the ductus 
cochlearis, and supporting other more highly specialized cells, 
known as the outer hair cells from the fact that they bear on their 
exposed surface a group of short hair-like processes. On the inner 
side of the tunnel is a single row of inner hair cells, similarly 
supported by adjoining epithelial cells. These hair cells are the 
structures which are stimulated by the sound vibrations and 
transmit the stimuli to the nerve endings (visible only with certain 
methods of staining) of the auditory nerve fibers. Show by 
diagram made from your study of the cross section the general features 
of the cochlea and of the spiral organ of Corti. 
1 This study of the Organ of Corti may conveniently be postponed until after the 
dissection of the ear (pp. 92-94). 
