The brain exists in all animals which have blood, and in those sea animals as well, which we have already mentioned as mollusks, although they are destitute of blood, the polypus, for instance. Man, however, has, in proportion to his body, the most voluminous brain of all. This, too, is the most humid, and the coldest of all the viscera, and is enveloped above and below with two membranous integuments, for either of which to be broken is fatal. In addition to these facts, we may remark that the brain is larger in men than in women. In man the brain is destitute of blood and veins, and in other animals it has no fat. Those who are well informed on the subject, tell us that the brain is quite a different substance from the marrow, seeing that on being boiled it only becomes harder. In the very middle of the brain of every animal there are small bones found. Man is the only animal in which it is known to palpitate[188] during infancy; and it does not gain its proper consistency until after the child has made its first attempt to speak. The brain is the most elevated of all the viscera, and the nearest to the roof of the head; it is equally devoid of flesh, blood, and excretions. The senses hold this organ as their citadel; it is in this that are centred all the veins which spring from the heart; it is here that they terminate; this is the very culminating point of all, the regulator of the understanding. With all animals it is advanced to the fore-part of the head, from the fact that the senses have a tendency to the direction in which we look. From the brain proceeds sleep, and its return it is that causes the head to nod. Those creatures, in fact, which have no brain, never sleep. It is said that stags[189] have in the head certain small maggots, twenty in number: they are situate in the empty space that lies beneath the tongue, and around the joints by which the head is united to the body. CHAP. 50.—THE EARS. ANIMALS WHICH HEAR WITHOUT EARS OR APERTURES.