Page:1888 Cicero's Tusculan Disputations.djvu/313

 if we examine thoroughly into the structure of the body, and the form and perfection of human nature. There are three things absolutely necessary for the support of life—to eat, to drink, and to breathe. For these operations the mouth is most aptly framed, which, by the assistance of the nostrils, draws in the more air. LIV. The teeth are there placed to divide and grind the food. The fore-teeth, being sharp and opposite to each other, cut it asunder, and the hind-teeth (called the grinders) chew it, in which office the tongue seems to assist. At the root of the tongue is the gullet, which receives whatever is swallowed: it touches the tonsils on each side, and terminates at the interior extremity of the palate. When, by the motions of the tongue, the food is forced into this passage, it descends, and those parts of the gullet which are below it are dilated, and those above are contracted. There is another passage, called by physicians the rough artery, which reaches to the lungs, for the entrance and return of the air we breathe; and as its orifice is joined to the roots of the tongue a little above the part to which the gullet is annexed, it is furnished with a sort of coverlid, lest, by the accidental falling of any food into it, the respiration should be stopped. As the stomach, which is beneath the gullet, receives the meat and drink, so the lungs and the heart draw in the air from without. The stomach is wonderfully composed, consisting almost wholly of nerves; it abounds with membranes and fibres, and detains what it receives, whether solid or liquid, till it is altered and digested. It sometimes contracts, sometimes dilates. It blends and mixes the food together, so that it is easily concocted and digested by its force of heat, and by the animal spirits is distributed into the other parts of the body. LV. As to the lungs, they are of a soft and spongy substance, which renders them the most commodious for