The first consists of levers; the second, of cylindrical tubes; and the third, of nervous particles. The first performs motion from place to place or locomotion; the second transmits and transmutes liquids, performing vascular action or nutrition; and the third transmits impressions from external objects, performing nervous action or thought. The motion of the first is extremely obvious; that of the second is barely apparent; and that of the third is altogether invisible. Not one of them can be confounded with another: for, considering their purposes only, it is evident that that which performs locomotion, neither transmits liquids nor sensations; that which transmits liquids, neither performs locomotion nor is the means of sensibility; and that which is the means of sensibility, neither performs locomotion nor transmits liquids. Now, the organs employed in locomotion are the bones, ligaments, and muscles; those employed in transmitting liquids or in nutrition, are the absorbent, circulating, and secreting vessels; and those employed about sensations or in thought, are the organs of sense, cerebrum, and cerebel, with the nerves which connect them. The first class of organs may, therefore, be termed locomotive, or (from their very obvious action) mechanical; the second, vascular or nutritive, or (as even vegetables, from their possessing vessels, have life) they may be termed vital; and the third may be named nervous or thinking, or (as mind results from them) mental. The human body, then, consists of organs of three kinds. By the first kind, locomotive or mechanical action is effected; by the second, nutritive or vital action is maintained; and by the third, thinking or mental action is permitted. Anatomy is, therefore, divided into three parts, namely, that which considers the mechanical or locomotive organs; that which considers the nutritive or vital organs; and that which considers the thinking or mental organs. Under the mechanical or locomotive organs are classed, first, the bones or organs of support; second, the ligaments or organs of articulation; and third, the muscles or organs of motion. Under the nutritive or vital organs are classed, first, the absorbent vessels or organs of absorption; second, the bloodvessels, which derive their contents from the absorbed lymph, or organs of circulation; and third, the secreting vessels, which separate various matters from the blood, or organs of secretion.[23] Under the thinking or mental organs are classed, first, the organs of sense, where impressions take place; second, the cerebrum or organ of thought, properly so called, where these excite ideas, emotions, and passions; and third, the cerebel or organ of volition, where acts of the will result from the last.[24] We may now more particularly notice the functions of these organs, which are the subject of physiology.