THE SENSES. 



567 



and the tickling sensation excited in the filaments of the fifth nerve, a 

 smell like of ammonia was excited by the negative pole, and an acid 

 odor by the positive pole; whichever of these sensations were produced, 

 it remained constant as long as the circle was closed, and changed to the 

 other at the moment of the circle being opened. Subjective sensations 

 occur frequently in connection with the sense of smell. Frequently a 

 person smells something which is not present, and which other persons 

 cannot smell; this is very frequent with nervous people, but it occasion- 

 ally happens to every one. In a man who was constantly conscious of a 

 bad odor, the arachnoid was found after death to be beset with deposits 

 of bone; and in the middle of the cerebral hemispheres were scrofulous 

 cysts in a state of suppuration. Dubois was acquainted with a man who, 

 ever after a fall from his horse, which occurred several years before his 

 death, believed that he smelt a bad odor. 



IV. Hearing. 



Anatomy of the Ear. For descriptive purposes, the Ear, or Organ 

 of Hearing, is divided into three parts, (1) the external, (2) the middle, 



FIG. 378 Diagrammatic view from before of the parts composing the organ of hearing of the 

 leftside. The temporal bone of the left side, with the accompanying soft parts, has been detach- 

 ed from the head, and a section has been carried through it transversely, so as to remove the front 

 of the meatus externus, half the tympanic membrane, the upper and anterior wall of the tympanum 

 and Eustachian tube. Ths meatus internus has also been opened, and the bony labyrinth exposed 

 by the removal of the surrounding parts of the petrous bone. 1, the pinna and lobe; 2, 2', meatus 

 externus; 2', membrana tympani; 3, cavity of the tympanum; 3', its opening backwards into the 

 mastqid cells; between 3 and 3', the chain of small bones; 4, Eustachian tube; 5, meatus internus, 

 containing the facial (uppermost) and the auditory nerves; 6, placed on the vestibule of the la by- 

 rinth above the fenestra ovalis; a, apex of the petrous bone; b, internal carotid artery; c, styloid 

 process; d, facial nerve issuing from the stylo-mastoid foramen; e, mastoid process ;/, squamous 

 part of the bone covered by integument, etc. (Arnold.) 



