=The Terminal Organs.=--"The membranous cochlea contains certain solid structures seated on the basilar membrane and forming the _organ of Corti_. This contains the end-organs of the cochlear nerves. Lining the sulcus spiralis, a groove in the edge of the bony lamina spiralis, are cuboidal cells; on the inner margin of the basilar membrane they become columnar, and then are succeeded by a row which bear on their upper ends a set of short stiff hairs, and constitute the _inner hair-cells_, which are fixed below by a narrow apex to the basilar membrane; nerve-fibres enter them. To the inner hair-cells succeed the _rods of Corti_ (_Co_, Fig. 21), which are represented highly magnified in Fig. 22. These rods are stiff and arranged side by side in two rows, leaned against one another by their upper ends so as to cover in a tunnel; they are known respectively as the _inner_ and _outer rods_, the former being nearer the _lamina spiralis_. The inner rods are more numerous than the outer, the numbers being about 6000 and 4500 respectively. Attached to the external sides of the heads of the outer rods is the _reticular membrane_ (_r_, Fig. 22), which is stiff and perforated by holes. External to the outer rods come four rows of _outer hair-cells_, connected like the inner row with nerve-fibres; their bristles project into the holes of the reticular membrane. Beyond the outer hair-cells is ordinary columnar epithelium, which passes gradually into cuboidal cells lining most of the membranous cochlea. From the upper lip of the sulcus spiralis projects the _tectorial membrane_ (_t_, Fig. 21) which extends over the rods of Corti and the hair-cells."[21] [Illustration: FIG. 23.--Sensory epithelium from ampulla or semicircular canal, and saccule. At _n_ a nerve-fibre pierces the wall, and after branching enters the two hair-cells, _c_. At _h_ a 'columnar cell' with a long hair is shown, the nerve-fibre being broken away from its base. The slender cells at _f_ seem unconnected with nerves. ] The hair-cells would thus seem to be the terminal organs for 'picking up' the vibrations which the air-waves communicate through all the intervening apparatus, solid and liquid, to the basilar membrane. Analogous hair-cells receive the terminal nerve-filaments in the walls of the saccule, utricle, and ampullæ (see Fig. 23).