SENSE OF HEARING. 615 



outer, to the head and neck of a swan. The feet of the rods 

 rest on the basilar membrane, and here may be seen the cells 

 from which they are derived ; their heads are joined together, 

 the head of the outer fitting into the depression of the inner. 

 Inasmuch as the rods are arranged in a series by the side of one 

 another, this arrangement makes a tunnel, the floor of which is the 

 basilar membrane, while the sloping sides are made by the inclined 

 rods. From each outer rod projects a phalangeal process. 



Reticular Lamina. This is also described under the name 

 membrane of Kolliker, and consists of a network in which are 

 perforations. It is made up of u minute fiddle-shaped cuticular 

 structures," phalanges, and through the perforations which are 

 between these phalanges project the cilia of the outer hair-cells. 



Outer Hair-cells. These are 12,000 in number, and are 

 arranged in three or four rows external to the outer rods, each 

 cell being surmounted by a bundle of short auditory hairs which 

 projects through one of the perforations of the reticular lamina. 

 From the. other extremity is given off a fine process which is 

 attached to the membrana basilaris. Between the rows of hair- 

 cells are the cells of Deitws, regarded as supporting cells, with 

 their bases on the membrana basilaris and their tapering processes 

 attached to the reticular lamina. 



Inner Hair-cells. These, 3500 in number, are arranged in a 

 single row, internal to the internal rods, and, like the outer hair- 

 cells, possess auditory hairs. The epithelial cells next to the 

 outer hair-cells are long and columnar, but cubical over the outer 

 wall of the canal of the cochlea ; they are much the same on the 

 inner side of the inner hair-cells, but are of the pavement 

 variety on the membrane of Reissner. 



Membrana Tectoria. This structure, called also the membrane 

 of Corti, is soft and fibrillated. It extends from the limbus, and 

 " lies like a pad over the organ of Corti," probably resting on the 

 auditory hairs. Retzius states that it is attached to the reticular 

 lamina. Gray says that it is blended with the ligamentum spirale 

 on the outer wall of the spiral canal. 



Auditory Nerve. The auditory nerve divides into two branches 

 at the bottom of the meatus auditorius internus ; these are the 

 cochlear and vestibular. 



Cochlear Branch of Auditoi*y Nerve. This is called also 

 cochlear nerve. At the base of the columella or modiolus of the 

 cochlea it subdivides into filaments, which run through it in 

 canals. When they reach the lamina spiralis they form at its 

 base the ganglion spirale, composed of a plexus of the nervous 

 filaments with ganglion-cells. From the ganglion spirale delicate 

 filaments are given off, which pass between the plates of the 

 lamina spiralis until they reach the sulcus spiralis, where they pass 

 out to the organ of Corti. Waldeyer states that here they divide 



