. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. i88 COMPARATIVE MORPHOLOGY OF VERTEBRATES. (whales, sirenians and some seals are exceptions) an external conch is developed behind the meatus to collect the sound waves and to direct them to the inner parts. In some birds the feathers are arranged around the meatus so as to play the same part. The conch is strength- ened by cartilage and is moved by muscles (fig. 142). There is evi- dence which points to the conch being homologous with either the operculum of fishes or with the first external gill of amphibians
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. i88 COMPARATIVE MORPHOLOGY OF VERTEBRATES. (whales, sirenians and some seals are exceptions) an external conch is developed behind the meatus to collect the sound waves and to direct them to the inner parts. In some birds the feathers are arranged around the meatus so as to play the same part. The conch is strength- ened by cartilage and is moved by muscles (fig. 142). There is evi- dence which points to the conch being homologous with either the operculum of fishes or with the first external gill of FIG. 188.—Diagram of mammalian ear. a, ampullae of semicircular canals; an, acustic nerve; en, cochlear nerve; em, external auditory meatus; eu, Eustachian tube;//, fenestra tympani; i, incus; m, malleus; p, perilymph space (black); pd, perilymph duct; ph, pharynx; s, stapes; sc, sacculus; sm, st, sv, scalae media, tympani et vestibuli; sg, spiral ganglion; t, tympanic cavity; tm, tympanic membrane; u, utriculus; v, vestibular nerve. Functions.—The vertebrate ear is primarily an organ of equi- libration by which the animal recognizes all changes of position. Though the purposes of the various parts are not accurately known, the following conclusions seem warranted. Every movement of the head affects the endolymph and the contained otoliths, causing them to move (by gravity or by momentum, or by both) over the cristae acusticae in the ampullae and thus to stimulate the sense cells and nerves. The position of the semicircular canals in approximately the three dimensions of space would seem to afford a means for the recognition of the directions and amounts of the components of any motion. The maculae, and especially that of the lagena, are probably concerned in the recognition of sound. In the fishes the lagena is poorly developed,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
