418 THE ORGAN OF TOUCH. 



two portions, a receiving and a nervous, the former being constructed on 

 the principles of optics in the one case, and of acoustics in the other. A 

 similar doubleness of structure may be recognized in the instance now 

 before us, though with a difference of effect, for in those cases the outer 

 or receiving organ is for the purpose of more powerfully concentrating 

 the influence received, but in touch it is the reverse. The office of the 

 cuticle, which covers over the true skin, is to render it less sensitive to 

 external impressions, and for this reason, therefore, it varies in thick- 

 ness in different regions, being less developed on those portions that are 

 more particularly devoted to tactile sensibility. Considering the hand, 

 Structure of or- or perhaps, more correctly, the tips of the ringers, as being 

 gan of touch, chiefly devoted to the purposes of touch, no construction 

 could be conceived of better adapted to that end. Placed at the extrem- 

 ity of the arm, a lever which is jointed at its middle, the elbow, and the 

 fore part of which has a motion of partial rotation, pronation, and supina- 

 tion upon its own axis, the hand being carried so that its palm presents 

 upward or downward, or in any of the intermediate positions included in 

 the half-circular motion -jointed again by the bones of the wrist, so as 

 to obtain a hinge-like movement, the hand may be flexed or extended 

 almost 180 degrees upon the forearm. Its bony structure, subdivided 

 into suitable pieces, is clothed with a multitude of muscles or their ten- 

 dons. In the fingers and thumb the structure breaks up into five sep- 

 arate pieces, possessed of an incredible firmness when we consider the 

 numberless motions which can be accomplished. The position and ar- 

 ticulation of the thumb, which enables it to set itself in opposition to 

 the other four digits, a feature which constitutes a hand, properly speak- 

 ing, gives the power of grasping things perfectly, and makes the whole 

 organ a perfect mechanism of prehension. The papillary structure, de- 

 veloped in its utmost refinement on the tips of the fingers, and fortified 

 behind by the nails, which present moderate resistance to pressures, com- 

 pletes this contrivance, which, from its perfect adaptation to 'the 'uses to 

 which it is devoted, its power, its delicacy, and the infinite movements 

 which it can accomplish, is not surpassed as an example of the adapta- 

 tion of means for the accomplishment of an end by any other structure 

 of the body. There have been authors who have asserted that the su- 

 periority of man over other animals may be entirely accounted for by his 

 possession of a hand a statement which, though it can not be main- 

 tained in its generality, is yet a very good proof of the appreciation in 

 which this wonderful instrument is held by those who have studied its 

 construction and functions most closely. 



Between the indications that have to be dealt with by the hand as 

 an organ of touch, and those dealt with by the eye and ear, there is an 

 essential, difference. The eye, for example, receives the pictures of ex- 



