658 SPECIAL SENSES. 



the answers were as frequently incorrect as they were correct ; but the dis- 

 crimination was easy and certain when the applications were made to the 

 surrounding healthy skin. When applications at a higher temperature were 

 made to the denuded part, the patient suffered only pain. 



The venereal sense is unlike any other sensation, and is general as well 

 as referable to the organs of generation. In this connection, however, it is 

 important to note that the tactile sensibility of the palmar surface of the 

 third phalanx of the fingers, measured by the sesthesiometer, compared with 

 the sensibility of the penis, is as 0-802 to 0-034, or between twenty-three and 

 twenty-four times greater. 



Ferrier has described a diffused tactile centre in the " hippocampal re- 

 gion," the action of which is crossed ; but the observations to determine the 

 loss of the sense of touch after destruction of this part, which were made 

 on monkeys, are by no means satisfactory. It must be very difficult to study 

 tactile sensibility in the inferior animals. 



OLFACTION. 



The nerves directly connected with the senses of olfaction, vision and 

 audition, have little or no general sensibility. As regards the olfactory 

 nerves, the parts to which they are distributed are so largely supplied with 

 branches from the fifth, that it is difficult to determine the fact of their sen- 

 sibility or insensibility to ordinary impressions. The olfactory nerves, how- 

 ever, are distributed to the mucous membrane of that portion only of the 

 nasal cavity, endowed with the special sense of smell. 



Nasal Fossce. The two irregularly shaped cavities in the middle of the 

 face, opening in front by the anterior nares and connected with the pharynx 

 by the posterior nares, are called the nasal fossae. The membrane lining 

 these cavities is generally called the Schneiderian mucous membrane, and 

 sometimes, the pituitary membrane. This membrane is closely adherent to 

 the fibrous coverings of the bones and cartilages by which the nasal fossse 

 are bounded, and it is thickest over the turbinated bones. It is continuous 

 with the membrane lining the pharynx, the nasal duct and lachrymal canals, 

 the Eustachian tube, the frontal, ethmoidal and sphenoidal sinuses and the 

 antrum. There are openings leading from the nasal fossae to all of these 

 cavities. 



The essential organ of olfaction is the mucous membrane lining the upper 

 half of the nasal fossae. Not only has it been shown anatomically that this 

 part alone receives the terminal filaments of the olfactory nerves, but physio- 

 logical experiments have demonstrated that it is the only part capable of ap- 

 preciating odorous impressions. If a tube be introduced into the nostril, 

 placed horizontally over an odorous substance so that the emanations can not 

 penetrate its caliber, no odor is perceived, though the membrane below the 

 end of the tube might receive the emanations ; but if the tube be directed 

 toward the odorous substance, so that the emanations can penetrate to the 

 upper portion of the nares, the odor is immediately appreciated. 



That portion of the lining of the nasal fossae, properly called the olfactory 



