THE SPECIAL SENSES AND SENSATIONS 277 



chamber, and the F^ustachian tube ; and the internal, of the bony 

 labyrinth containing the membranous labyrinth which is sur- 

 rounded by the perilymph, and which contains the endolymph. 



7. The internal ear consists of three parts : the vestibule, 

 the semicircular canals, and the cochlea. The auditory nerve 

 sends fibers to all these parts. 



8. Sound waves are caught by the concha and directed in 

 through the auditory canal ; they beat against the drumhead, 

 causing it to vibrate ; this imparts its motion to the chain of 

 bones which intensify, modify, and focus the vibrations upon 

 the oval window ; here the vibrating membrane communicates 

 its movement to the liquids of the ear which act upon the 

 membranous labyrinth ; and this excites the ends of the audi- 

 tory nerves. 



9. The ear is a very delicate and complicated organ and 

 should receive a certain amount of care daily. If in good 

 health, the chief caution is : Keep the concha clean and do not 

 meddle with the auditory canal. 



10. The eye is the end organ of sight. The eyeball consists 

 of three layers : the sclerotic coat and cornea, the choroid and 

 iris, and the retina. The globe is filled with the aqueous 

 humor, the lens, and the vitreous humor. The cornea is trans- 

 parent, and the iris has an opening at its center, the pupil, 

 which determines the amount of light that shall enter. 



11. The eyeball has six large muscles which turn it in all 

 directions, and many small muscles which adjust the eye for far 

 and near objects. 



12. The eye is protected by the eyelids, eyelashes, eye- 

 brows, lachrymal glands, tear ducts, and by the orbit itself. 



13. The rays of light from an object pass through the 

 cornea, the aqueous humor, the pupil of the iris, the lens, the 

 vitreous humor, and are focused on the yellow spot of the 

 retina. The impressions are then carried to the occipital lobe 

 of the brain over the great optic nerve. 



