CHAPTER XXIV 



THE SENSE OF SIGHT. THE VOICE 



The eye is the organ of sight. It is situated in the orbital 

 fossa resting in a collection of adipose tissue from which it is 

 separated by the capsule of Tenon. This is a thin fascia surround- 

 ing the greater part of the eyeball, and making a " flexible pocket" 

 or lymph space in which the ball can be freely moved. The eye 

 is a sphere or globe having at its surface three layers called the 

 coats .or tunics of the eye namely the solera and cornea (fibrous) , 

 forming the outer coat, the choroid and iris (vascular), forming 

 the middle coat, and the retina (nervous) the inner coat. They 



Retina 



Choroid 



Sclera 



Cornea 



Iris 



Ciliary processes 



Lymph canal 

 Ciliary muscle 



FIG. 214. A SECTION OF THE EYE. (H olden.) 



i, Anterior chamber; 2, posterior chamber. The aqueous humor occupies the two 



chambers. 



contain three transparent structures the aqueous humor, crystal- 

 line lens and vitreous body. 



The sclera is the "white of the eye." It is dense and tough, 

 protecting the more delicate structures within. One-sixth of the 

 surface of the ball in front is occupied by the cornea instead of 

 the sclera, and this also is dense and tough, but transparent for 

 the admission of light. It contains no blood-vessels, but many 

 tiny lymph-spaces. It is the most prominent part of the eyeball, 



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