98 PRACTICAL PHYSIOLOGY 



of the retina can be traced as far as these processes, where it terminates 

 with a wavy edge, the ora serrata. 



5. Remove carefully the vitreous humour, and note that it adheres 

 to the ciliary processes by its outer coat, the hyaloid membrane. On 

 removing the vitreous from the more central portion, note that it 

 appears adherent to the posterior surface of the lens. The posterior 

 layer of the lens capsule is continuous with the hyaloid membrane. If 

 necessary, cut away the vitreous humour so as not to dislocate the 

 lens. 



6. Make a radial incision from the edge of the sclerotic down to the 

 edge of the lens. Carefully separate the iris and ciliary region from the 

 lens, and the suspensory ligament will be seen passing from the ciliary 

 body mainly towards the front surface of the lens. Carefully separate 

 the lens from this, and the suspensory ligament continuous with the 

 capsule of the lens will float up away from the iris. 



7. Cut round the upper half of cornea near its junction with the 

 sclerotic. The anterior chamber will be exposed containing a clear 

 fluid, the aqueous humour. Note the thickness of the cornea. At the 

 back of the anterior chamber is seen the black curtain of the iris, with 

 its central aperture the pupil. 



8. Notice that the fresh vitreous humour and lens when placed in 

 water are not easily seen ; they have almost the same refractive index 

 as water. After death the lens slowly becomes turbid. 



9. Hold up the lens and look through it towards a lighted match ; 

 it will give an inverted image. 



10. Notice the segmentation of the lens; it is peculiar, and may be 

 roughly compared to a segmentation similar to that of an orange com- 

 bined with the concentric lamination of an onion. 



CHAPTER XXVI. 

 THE REFRACTING MEDIA OF THE EYE. 



Kuhne's Artificial Eye. The nature of the refraction produced by 

 the various media of the eye is conveniently illustrated by means of 

 this instrument (Fig. 93). It consists of an oblong box, one of the 

 long vertical sides being generally made of opaque material, the other 

 of glass. The front end of the box is bounded by a curved glass 

 surface, the hinder end is a plane sheet of glass. Various accessories 

 are supplied with the instrument, such as a double convex lens which 

 can be placed in the axis of the box behind the cornea, a frosted glass 



