3410. What the Bird is, it is by virtue of its feathers. It is throughout a trachea, a pair of bellows. Its bones are hollow, full of air, and stand likewise in communication with the lungs; the feather-quills are also hollow.
Senses.
3411. The wings have all the muscles to themselves; the bone has in them gone to ruin. On the legs, on the contrary, the muscles have declined, and the bone has got the upper hand.
Hence it results, properly speaking, that only the thoracic members are perfected, because the Bird is nothing but thorax. The abdomen has, so to speak, vanished, and through this the abdominal limbs are left only, as thin and dry poles or staffs.
3412. From the same cause the muscular flesh upon the head has disappeared. Neck and head are lean, or like Insect horn, which serves only the nervous system.
3413. Beyond the excess of motion the sense of feeling has been nearly lost. The toes are simply destined for motion, and to be used as scrapers, and the digits have become the supports of feathers.
3414. The bill is an Insect's proboscis. In the Bird no teeth whatever project from the flesh, but the jaws themselves. To such an extent has the flesh been withdrawn. What has been called the cere is the only remnant of the facial flesh. Even nostrils and tongue have suffered ossification.
3415. The tongue is a feather. Saliva is scarcely present.
3416. The ears, as being the sense of motion, are far more perfectly evolved than in all the preceding classes. They have opened outwards, and possess an additional auditory part, the cochlea.
With the limbs the sense of hearing must of necessity grow perfect.