CONTENTS. , IX 



PAGE 



Lachrymal apparatus. Vision; functions of the retina, .re- 

 versed images ; functions of the iris ; optic centre, visual angle, 

 visual impressions, single or mixed, adaptation of the eye to dis- 

 tances, myopia, presbyopia ; achromatism ; single and double 

 vision with two eyes, stereoscope; alternation in the action of 

 the eyes ; persistence of impressions on the retina ; accidental 

 images ; irradiation ; accidental aureola ; Daltonism ; apparent 

 motion of objects! Optic nerve. Movements of the eye. Ex- 

 tent of vision, 152 



CHAPTER XII. 



Sense of hearing. Organ of hearing. External ear; pavilion of 

 the ear, auditory canal. Middle ear; tympanum, drum, or 

 membrana tympani, fenestra ovalis, fenestra rotunda, Eustachian 

 tube, the small bones of the ear, muscles and movements of the 

 small bones. Internal ear; labyrinth, vestibule, semicircular 

 canals, cochlea, membranous labyrinth. Auditory nerve. 

 Noises and sounds; duration, pitch, intensity and quality of 

 sound ; passage of sound through air, water, solid bodies ; 

 gravity, sharpness of sound. Mechanism of hearing; functions 

 of different parts of the ear; movement of sounds in the ear; 

 propagation of sounds to the auditory apparatus by the vibrations 

 of the bones of the skull. Opinions of physiologists on the 

 functions of different portions of the labyrinth ; theory of Helm- 

 holtz. Fineness and delicacy of hearing. Correctness of the 

 ear. Estimation of the intensity, the distance, and the direction 

 of sounds; ventriloquism. Duration of auditory impressions. 

 Sensations having an internal origin. Parallel between the eye 

 and ear, 182 



CHAPTER XIII. 



Sense of smell. Olfactory organs. Nose; nasal fossae, turbinated 

 bones, pituitary membrane. Olfactory nerve. Odoriferous 

 principles ; their development, their action on the nervous sys- 

 tem. Smell, its seat ; duration of olfactory impressions. Uses, 

 and acuteness of smell, 203 



CHAPTER XIV. 



Sense of taste. Organ of taste. Special nerves of the organ. 

 Flavours. Taste, 210 



CHAPTER XV. 



Sense of touch. Difference between touch and feeling. Tactile 

 sensibility and general sensibility. Organ of touch. Sensation 

 of contact ; difference in the sensibility of different regions of the 

 body; simple contact, shock, vibration. Sensation of pressure; 



