XX CONTENTS. 



CHAPTER XXXII. 



VISION. 



PAGE 



The Construction of the Eyeball, 555 



Dioptric Media of the Eyeball, 558 



Structure of the Lens, 560 



The Dioptrics of the Eye, 562 



Accommodation, 568 



Defects of Accommodation, 571 



Defects of Dioptric Apparatus, ; 572 



The Iris, 574 



The Ophthalmoscope, .... 577 



Visual Impressions, 578 



The Function of the Retina 579 



Color Perceptions, . 586 



Mental Operations in Vision 589 



Movements of the Eyeballs, 590 



Binocular vision, 592 



CHAPTER XXXIII. 

 HEARING. 



Sound 594 



Conduction of Sound vibrations through the Outer Ear, . . . 598 



Conduction through the Tympanum, 601 



Conduction through the Labyrinth, 603 



Stimulation of the Auditory Nerve, . 607 



CHAPTER XXXIV. 



CENTRAL NERVOUS ORGANS. 



Nerve Cells, 611 



Thf Spinal Cord as a Conductor, 614 



The Spinal Cord as a Collection of Nerve Centres, .... 616 



Sj>.vi;il Kdlex Centres, 625 



Automatism, 626 



CHAPTER XXXV. 



THK MEDULLA OBLONG ATA. 



The Medulla Oblongata as a Conductor, 628 



The Respiratory Centre, , 630 



