. Comparative anatomy and physiology. Chap, xii.] EAR OF 'MAMMALS. 471 continued into a tube which enters into connection with the subarachnoid cerebral cavity. Eight different sensory regions are now to be distinguished; the cochlear region lias a commencing outgrowth or lagena, and within is a space which is covered over by a very thin membrane, the membrana basilaris. In the Reptilia we observe several stages in the outgrowth of the cochlea, and these are most marked in crocodiles, which, in this character, as in so many others, stand nearest to the birds. In these last the lagena is quite
. Comparative anatomy and physiology. Chap, xii.] EAR OF 'MAMMALS. 471 continued into a tube which enters into connection with the subarachnoid cerebral cavity. Eight different sensory regions are now to be distinguished; the cochlear region lias a commencing outgrowth or lagena, and within is a space which is covered over by a very thin membrane, the membrana basilaris. In the Reptilia we observe several stages in the outgrowth of the cochlea, and these are most marked in crocodiles, which, in this character, as in so many others, stand nearest to the birds. In these last the lagena is quite prominent (Fig. 198; B, &), and begins to take on a spiral course. With the exception of the Prototheria, all Mammals have their cochlea coiled into a heliciform spiral, the canal of which is wound round the bony axis or modiolus; the coil may be flat, as in the Cetacea, or very steep, as in some Rodents (guinea-pig) (Fig. 198 ; c). The internal structure of the cochlea has been fully described in the " Elements of Histology " (chap, xii.) ; here it need only be said that the scala vestibuli, the membrane of Reissner, and the rods of Corti are peculiar to the mammalian ear; as to the last, we have so far evidence that it has been developed within the limits of the mammalian series that we find them to be much more simply arranged in the Prototheria than in the higher mammals. The absence of this organ from the ears of birds, Fig> many of which are, as we know, of Cod. capable of being attracted by musical sounds, makes it impossible for us at present to accept the doctrine that these rods are physiologically impor- tant as the means of distinguishing different notes of music. The otoliths found in the lymph of the membranous labyrinth are ordinarily larger in fishes than in higher. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrat
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