species of action, but propagates it widely to new existences in the manner just described. In the thinking functions, the organs of sense receive external impressions, which excite in them sensations; the cerebrum, having these transmitted to it, performs the more complicated functions of mental operation, whence result ideas, emotions, and passions; and the cerebel, being similarly influenced, performs the function of volition, or causes the acts of the will. It is not unusual to consider the body as being divided into the head, the trunk, and the extremities; but, in consequence of the hitherto universal neglect of the natural arrangement of the organs and functions into locomotive, nutritive, and thinking, the beauty and interest which may be attached to this division, have equally escaped the notice of anatomists. It is a curious fact, and strongly confirmative of the preceding arrangements, that one of these parts, the extremities, consists almost entirely of locomotive organs, namely, of bones, ligaments, and muscles; that another, the trunk, consists of all the greater nutritive organs, namely, absorbents, bloodvessels, and glands; and that the third, the head, contains all the thinking organs, namely, the organs of sense, cerebrum, and cerebel.[25] It is a fact not less curious, nor less confirmative of the preceding arrangements, that, of these parts, those which consist chiefly of locomotive or mechanical organs--organs which, as to mere structure, and considered apart from the influence of the nervous system over them, are common to us with the lowest class of beings, namely, minerals[26]--are placed in the lowest situation, namely, the extremities; that which consists chiefly of nutritive or vital organs--organs common to us with a higher class of beings, namely, vegetables[27]--is placed in a higher situation, namely, the trunk; and that which consists chiefly of thinking or mental organs--organs peculiar to the highest class of beings, namely, animals[28]--is placed in the highest situation, namely, the head. It is not less remarkable, that this analogy is supported even in its minutest details; for, to choose the nutritive organs contained in the trunk as an illustration, it is a fact, that those of absorption and secretion, which are most common to us with plants, a lower class of beings, have a lower situation--in the cavity of the abdomen; while those of circulation, which are very imperfect in plants,[29] and more peculiar to animals, a higher class of beings, hold a higher situation--in the cavity of the thorax.