480 THE SPECIAL SENSES. 



tion is fully performed by various other parts of the body. Thus 

 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 highly developed nervous papilla : in some of the monkeys the 

 extremity of the prehensile tail, and in the elephant the end of the 

 nose, which is developed into a flexible and sensitive proboscis, is 

 employed as an organ of touch. This function, therefore, may be 

 performed by either 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 dependent 

 mainly upon branches of the fifth pair. In the neck, trunk, and 

 extremities it is due to the sensitive fibres of the cervical, dorsal, 

 and lumbar spinal nerves. It exists also, to a considerable extent, 

 in the mucous membranes of the mouth and nose, and of the pas- 

 sages leading from them to the interior of the body. In these 

 situations, it depends upon the sensitive filaments of certain of the 

 cranial nerves, viz., the fifth pair, the glosso-pharyngeal, and the 

 pneumogastric. The sensibility of the mucous membranes is most 

 acute in those parts supplied by branches of the fifth pair, viz., the 

 conjunctiva, anterior part of the nares, inside of the lips and cheeks, 

 and the anterior two-thirds of the tongue. At the base of the 

 tongue and in the fauces, where the mucous membrane is supplied 

 by filaments of the glosso-pharyngeal nerve, the general sensibility 

 is less perfect; and finally it diminishes rapidly from the upper 

 part of the oesophagus and the glottis toward the stomach and the 

 lungs. Thus, we can appreciate the temperature and consistency 

 of a foreign substance very readily in the mouth and fauces, but 

 these qualities are less distinctly perceived in the oesophagus, and 

 not at all in the stomach, unless the foreign body happen to be 

 excessively hot or cold, or unusually hard and angular in shape. 

 The general sensibility, which is resident in the skin and in a certain 

 portion of the mucous membranes, diminishes in degree from with- 

 out inward, and disappears altogether in those organs which are 

 not supplied with nerves from the cerebro-spinal system. 



It is particularly to be observed, however, that while the general 

 sensibility of the skin, and of the mucous membranes above men- 

 tioned, varies in acuteness in different parts of the body, it is every- 

 where the same in kind. The tactile sensations, produced by the 

 contact of a foreign body, are of precisely 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. 



