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PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



scala vestibuli, while the other, or inferior, terminates in the round 

 window and is called the scala tympani. On these laminae spirales are 

 distributed portions of the auditory nerve, which takes origin from the 

 floor of the fourth ventricle and runs into the petrous portion of the 

 temporal bone through the meatus auditorius internus and divides into 

 two divisions, one going to the cochlea and the other to the vestibule 

 near to the end of the semicircular canals. It loses itself upon the walls 

 of the vestibule and the walls of the ampullae, or membranous dilatations 

 at the commencement of the three semicircular canals (Fig. 406). 



The cochlear nerve is distributed to the scalae of the cochlea, where 

 its terminal fibres form connection with Corti's organ, which is placed 



Fig. 406.— Scheme of the Labyrinth and Termination op the Auditory 

 Nerve. {Landois.) 



I. Transverse section of a tnrn of the cochlea. II. A. ampulla of a semicircular canal : a d auditorv 

 cells, p. provided with a fine hair ; T. otoliths. III. Scheme of the human labyrinth IV Scheme of 

 a bird's labyrinth. V. Scheme of a fish's labyrinth. 



in the ductus cochlearis, a small, triangular chamber; cut off from the 

 scala vestibuli by the membrane of Reissner (Fig. 407). 



Corti's organ is placed on the membranous portion of the lamina 

 spiralis, and consists of an apparatus composed of the so-called Corti's 

 arches, each of which consists of two Corti's rods. Every two rods 

 unite to form an arch, so that there are always two or three inner rods 

 and two outer rods. Toward the apex of the cochlea the rods become 

 longer and the span of the arches increases. The terminal organs of 

 the cochlear nerve are the cylindrical hair-cells described by Corti, of 

 which there are two rows, the row of inner cells resting on a layer of 

 small, granular cells, and the outer cells distributed in three or four rows 

 resting on a basement membrane. Between the outer cells there are 



