2483. The ear has not only a nerve, but likewise a brain, of its own.
2484. The cerebellum is the auditory brain, and from it the acoustic nerves take their rise. For, since the ear is the sense of the whole motor system, and consequently of half the animal, it inevitably follows, that an appropriate or special nervous mass must be developed for it, just as the myelon or spinal chord has been for the trunk. An organ, which is so constantly active, must necessarily have a large nervous mass. The cerebellum is consequently not a brain in the general sense, but one which is wholly individualized. It participates in the motion, which, as sound, is transmitted to the animal.
2485. By its signification as well as by its own brain, the ear gives us to recognize its elevated rank above the other senses.
2486. The ear must stand in relation with the body's limbs.
2487. The ears first make their appearance in animals, associated with a tolerable development of the limbs. With the exception of a few instances, the ears first become apparent in Fishes, being in them at least furnished for the first time with true ossicles and semicircular canals. The ear, like the limbs, with which it constantly maintains a parallel course, is very slowly perfected. In the Fishes which have only fins (as instruments of locomotion) it is wholly concealed within the cranial bones; in the Reptiles it emerges or is more exposed to view; but for the first time in Birds and Mammalia where, generally speaking, the limbs also are first perfected, it attains its completion; in them only is the cochlea fully developed, and an auditory meatus which opens externally.
5. Nervous Sense.
2488. In all lower organs, and even in the senses which have hitherto been commented upon, the nervous system was not the chief, but only the co-ordinate agent. It has only by its conjunction with, assisted in elevating the character of, other systems, so that their material might be converted into spiritual processes. But the nervous is also a self-substantial system, and must therefore attain likewise a free development.
2489. With the highest organs of the nervous system, the relation which has been hitherto maintained, must be reversed. The inferior systems will now be the co-ordinate agents.
2490. The highest nervous organ can only possess that function, which is originally peculiar to the nervous system, i. e. the most delicate polarization, the light-function. There is the Light-sense.
2491. The eye is nothing but a nervous system represented in a state of purest organization, just as the ear was the purest system of motion.