CHAPTER XXVI 

 THE ORGAN OF VISION 



Optic (second nerve) General properties of the optic nerves Physiological anatomy of the 

 eyeball Sclerotic coat Cornea Choroid coat Ciliary processes Iris Pupillary 

 membrane Retina Layer of rods and cones (Jacob's membrane, or bacillar mem- 

 brane) Crystalline lens Suspensory ligament of the lens (zone of Zinn) Aqueous 

 humor Vitreous humor Summary of the anatomy of the globe of the eye. 



THE chief points to be considered in the physiology of vision are the 

 following : 



1. The physiological anatomy and the general properties and uses 

 of the optic nerves. 



2. The physiological anatomy of the parts essential to normal vision. 



3. The laws of refraction, diffusion etc., bearing on the physiology 

 of vision. 



4. The action of the different parts of the eye in the production and 

 appreciation of correct images. 



5. Binocular vision. 



6. The physiological anatomy and uses of accessory parts, as the 

 muscles that move the eyeball. 



7. The physiological anatomy and uses of the parts that protect the 

 eye, as the lachrymal glands, eyelids etc. 



OPTIC (SECOND NERVE) 



The bands that pass from the tubercula quadrigemina to the eyes 

 are divided into the optic tracts, which extend from the tubercula on 

 either side to the chiasm, or commissure ; the chiasm, or the decussat- 

 ing portion ; and the optic nerves, which pass from the chiasm to the 

 eyes. 



The optic tracts arise each by two roots, internal and external. The 

 internal roots, which are the smaller, arise from the anterior tubercula 

 quadrigemina and pass through the internal corpora geniculata to the 

 optic chiasm. The external roots, which are the larger, arise from the 

 posterior part of the optic thalami, pass to the external corpora geni- 

 culata, from which they receive fibres, and thence to the chiasm. 



Partly by anatomical researches and partly by experiments on the 



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