these spirits there be three kinds, according to the three principal parts, brain, heart, liver; natural, vital, animal. The natural are begotten in the liver, and thence dispersed through the veins, to perform those natural actions. The vital spirits are made in the heart of the natural, which by the arteries are transported to all the other parts: if the spirits cease, then life ceaseth, as in a syncope or swooning. The animal spirits formed of the vital, brought up to the brain, and diffused by the nerves, to the subordinate members, give sense and motion to them all. SUBSECT. III.—_Similar Parts_. _Similar Parts_] Containing parts, by reason of their more solid substance, are either homogeneal or heterogeneal, similar or dissimilar; so Aristotle divides them, lib. 1, cap. 1, de Hist. Animal.; Laurentius, cap. 20, lib. 1. Similar, or homogeneal, are such as, if they be divided, are still severed into parts of the same nature, as water into water. Of these some be spermatical, some fleshy or carnal. [957]Spermatical are such as are immediately begotten of the seed, which are bones, gristles, ligaments, membranes, nerves, arteries, veins, skins, fibres or strings, fat. _Bones_.] The bones are dry and hard, begotten of the thickest of the seed, to strengthen and sustain other parts: some say there be 304, some 307, or 313 in man's body. They have no nerves in them, and are therefore without sense. A gristle is a substance softer than bone, and harder than the rest, flexible, and serves to maintain the parts of motion. Ligaments are they that tie the bones together, and other parts to the bones, with their subserving tendons: membranes' office is to cover the rest. Nerves, or sinews, are membranes without, and full of marrow within; they proceed from the brain, and carry the animal spirits for sense and motion. Of these some be harder, some softer; the softer serve the senses, and there be seven pair of them. The first be the optic nerves, by which we see; the second move the eyes; the third pair serve for the tongue to taste; the fourth pair for the taste in the palate; the fifth belong to the ears; the sixth pair is most ample, and runs almost over all the bowels; the seventh pair moves the tongue. The harder sinews serve for the motion of the inner parts, proceeding from the marrow in the back, of whom there be thirty combinations, seven of the neck, twelve of the breast, &c. _Arteries_.] Arteries are long and hollow, with a double skin to convey the vital spirit; to discern which the better, they say that Vesalius the anatomist was wont to cut up men alive. [958]They arise in the left side of the heart, and are principally two, from which the rest are derived, aorta and venosa: aorta is the root of all the other, which serve the whole body; the other goes to the lungs, to fetch air to refrigerate the heart. _Veins_.] Veins are hollow and round, like pipes, arising from the liver, carrying blood and natural spirits; they feed all the parts.