(From to turn round). Called also antrum buccinosum. The first mention made of this part of the ear is by Plutarch, who says, that Empedocles, a scholar of Pythagoras, was acquainted with it and its use, for he said that sounds were formed there. It is a winding cavity, which turns round a nucleus in a spiral manner. It is larger where it begins, becoming smaller like a horn; the second turns almost within the first, and the third within the second, making about two turns and a half. It is divided into a superior and an inferior cavity, by a partition in the middle, perpendicular to the axis of the spindle of the cochlea, so that in reality it consists of two semi canals: that part of the partition next to the axis is bony, which terminates in an edge, where it is membranous; it grows narrower towards the apex. The scala, which is next the basis, opens into the tympanum by the fenestra rotunda; that towards the apex into the vestibulum by the fenestra ovalis.
That the cochlea is a part of the organ of hearing may be concluded from its spiral laminae, which are hard, dry, slender, and easily broken; conditions required in bodies susceptible of tremulous motions. Again, when the large branch of the portio mollis of the seventh pair of nerves arises at the basis of the cochlea, it is divided into a great number of smaller branches, which, passing through all the smaller meatuses with which the spindle is perforated, are distributed to the various windings and meanders of these spiral laminae, where they are lost. These laminae are not only calculated for receiving the vibratory motion of the air, but their structure has been looked on as a convincing proof that this part of the organ is qualified and disposed for accommodating itself to the different characters and degrees of sounds; for since it is broader at the beginning of its first circumvolution than at the extremity of its last, and since the breadth of its other parts is in like manner proporlionably diminished, its broadest parts are supposed to be fit for the reception of those slow and languid vibrations, which are productive of grave tones, since they may be put into a commotion without the other parts undergoing any change; and, vice versa, that when its narrower parts are struck, their vibrations are brisk and lively, and consequently produce acute tones. Therefore, according to the various commotions of the spiral laminae, the nerves distributed through its substance may probably receive the various impressions of the air, which exhibit and represent various tones or modulations of sound. See Sonus.
Co"Chlea Celata. See Ardrosace.
Cochlea fossilis and lapide'a. See Cochlita.