Those among the horned animals which have teeth in one jaw only, and pastern bones on the feet, produce tallow or suet. Those, on the other hand, which are cloven-footed, or have the feet divided into toes, and are without horns, have simple fat only. This fat becomes hard, and when quite cold turns brittle, and is always found at the extremity of the flesh; while, on the other hand, the fat which lies between the skin and the flesh forms a kind of liquid juice. Some animals naturally do not become fat, such as the hare and the partridge, for instance. All fat animals, male as well as female, are mostly barren; and those which are remarkably fat become old the soonest. All animals have a certain degree of fatness in the eyes. The fat in all animals is devoid of sensation, having neither arteries nor veins. With the greater part of animals, fatness is productive of insensibility; so much so, indeed, that it has been said, that living swine have been gnawed even by mice.[308] It has been even asserted that the fat was drawn off from the body of a son of L. Apronius, a man of consular rank, and that he was thus relieved of a burden which precluded him from moving. CHAP. 86.—THE MARROW: ANIMALS WHICH HAVE NO MARROW. The marrow seems also to be formed of a similar material; in the young it is of a reddish colour, but it is white in the aged. It is only found in those bones which are hollow, and not in the tibiæ of horses or dogs; for which reason it is, that when the tibia is broken, the bone will not reunite, a process which is effected[309] by the flow of the marrow. The marrow is of a greasy nature in those animals which have fat, and suetty in those with horns. It is full of nerves, and is found only in the vertebral column[310] in those animals which have no bones, fishes, for instance. The bear has no marrow; and the lion has a little only in some few bones of the thighs and the brachia, which are of such extraordinary hardness that sparks may be emitted therefrom, as though from a flint-stone. CHAP. 87.—BONES AND FISH-BONES: ANIMALS WHICH HAVE NEITHER. CARTILAGES.