THE PHYSIOLOGY OF VISION. 



CHAPTER XXV. 

 THE DISSECTION OF THE EYE. 



THIS can be conveniently carried out on the fresh eye of an ox or 

 sheep. 



1. Notice in the front of the eye the transparent circular area, the 

 cornea, continuous with the greyish opaque border, the sclerotic. This 

 coat is continued over the sides and back of the eye, but will be found 

 covered with fat. The external eye muscles may be traced in the fat, 

 and their tendinous insertion seen in the front of the sclerotic. The 

 optic nerve will be seen penetrating posteriorly. The greyish surface of 

 the sclerotic in front is covered by a thin membrane, the conjunctiva, 

 which is continued as a lining for the eyelids. 



2. Having removed the fat from a portion of the upper surface of the 

 eye so as to expose the sclerotic, make a pair of incisions passing along 

 the surface from before backwards, and starting a few millimetres 

 behind the corneo-sclerotic junction, let these incisons meet posteriorly. 

 Then carefully peel up the sclerotic towards the cornea. Observe the 

 dark underlining of the sclerotic, the lamina fusca. Note the choroid 

 now exposed, and anteriorly observe that it is covered by a number of 

 pale fibres passing forward to the corneo-sclerotic junction, forming the 

 ciliary muscle. 



3. Remove carefully the piece of the choroid lying exposed, and note 

 a pale membrane lying beneath, the retina. 



4. Place the eye in a glass basin of water, and make an incision right 

 round the eye through all the coats, so as to separate the posterior from 

 the anterior half. Examine the posterior half in the water. Note the 

 thin retina floating away from the choroid, eccentrically in this the 

 optic disc where the optic nerve enters the eye, and the blood-vessels 

 radiating from this region. The vitreous humour of jelly-like consist- 

 ency will remain attached to the anterior half of the eye. Looking 

 through this, note the crystalline lens, at the side of this the radial 

 folds of the choroid forming the ciliary processes. The thick portion 



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