596 THE SENSES. 



when applied to the tips of the fingers, though it will produce no impres- 

 sion on the rest of the limbs or trunk ; and one which is too faint to be 

 distinguished by the fingers may be perceptible at the tip of the tongue. 



Certain parts of the body, furthermore, are especially well adapted 

 for use as organs of touch, not only on account of their acute sensibility, 

 but also owing to their conformation and mobility. In man, the hands 

 are the most favorably constructed for this purpose, by the numerous 

 articulations and varied power of movement of the fingers, b} r wMch 

 they may be applied to solid surfaces of any form, and brought succes- 

 sivelj T in contact with all their irregularities and depressions. We are 

 thus enabled to obtain the most precise information as to the texture, 

 consistency, and configuration of foreign bodies. 



But the hands are not the exclusive organs of touch, even in man, 

 and in the lower animals the function is mainly performed by other parts. 

 In the cat and in the seal, the long bristles seated upon the lips are used 

 for this purpose, each bristle being connected at its base with a nervous 

 papilla ; and in the elephant the end of the nose, which is developed 

 into a flexible and sensitive proboscis, is employed as the principal organ 

 of touch. This function, therefore, may be performed by one part of 

 the body or another, provided the accessory organs be developed in a 

 favorable manner. 



About the head and face, the sensibility of the skin is principally de- 

 pendent upon branches of the fifth pair. In the neck, trunk, and extre- 

 mities it is due to the sensitive fibres of the cervical, dorsal, and lumbar 

 spinal nerves. It exists, to a considerable extent, in the mucous mem- 

 branes of the mouth and nose, and of other passages leading to the in- 

 terior. The sensibility of the mucous membranes is most acute in parts 

 supplied by branches of the fifth pair, namely, the conjunctiva, anterior 

 part of the nares, inside of the lips and cheeks, and the anterior two- 

 thirds of the tongue. The tactile sensibility, which is resident in the 

 skin and in a certain portion of the mucous membranes, diminishes in 

 degree from without inward, and disappears altogether in the internal 

 organs which are not abundantly supplied with nerves from the cerebro- 

 spinal sj'stem. 



While the general sensibility of the skin, and of the mucous mem- 

 branes, varies in acuteness in different parts of the bod3 r , it is every- 

 where the same in kind. The tactile sensations produced by the con- 

 tact of a foreign body are of the same nature, whether they be felt by 

 the tips of the fingers, the dorsal or palmar surfaces of the hands, the 

 lips, cheeks, or any other part of the integument. Their only difference 

 is in the intensity and distinctness of the impressions produced. 



The appreciation of the weight or mass of a foreign body is obtained 

 from the degree of pressure which it causes upon the integument, when 

 supported by the hand or other part of the body. It does not appear 

 that any other kind of sensation is necessary for this purpose, although 

 we generally also employ, in estimating a weight, the degree of muscular 

 effort required to sustain it. If the hand, however, be rested upon some 



