DISSECTION OP THE EYEBALL. 265 



5. The Inner Nuclear Layer contains spindle-shaped or bipolar nerve 

 cells with distinct oval nuclei and only a small amount of protoplasm. 

 The inner and outer poles of the cells are continued through the 4th 

 and 6th layers respectively. 



6. The Outer Molecular Layer repeats the structure of the inner 

 molecular layer. 



7. The Outer Nuclear Layer contains spindle-shaped cells with con- 

 spicuous nuclei and a small amount of protoplasm, the poles of the cells 

 being prolonged as in the case of the similar elements in the inner 

 nuclear layer. 



8. The Memhrana Limitans Externa. — This is the outer boundary of 

 the sustentacular framework of fibres already mentioned. 



9. The Layer of Rods and Cones, or the hacillary layer, is composed 

 of two different kinds of elements. The longer elements, the rods, 

 extend vertically between the 8th and 10th layers; the cones are much 

 shorter than the rods, and do not reach so far as the next layer. 



10. The Pigmented Epithelium. — This is a layer of polygonal pig- 

 mented cells, generally six-sided. 



Directions. — The third eye should be transversely divided with a 

 sharp scalpel, about half an inch behind the junction of the sclerotic 

 and cornea. This should be done with the eye immersed in water. 

 The posterior half, after removal of the vitreous humour, shovild be used 

 for the better examination of the inner surface of the retina. The lens 

 should be removed for examination from the anterior half In the eye 

 already used for the display of the retina, that coat should be in part 

 removed, so as to display the vitreous humour with the lens imbedded 

 in its anterior part. By a combined examination of all the pi'eparations, 

 the following points regarding the lens and vitreous body may be made 

 out. 



The Lens is situated behind the pupil, and is contained within a 

 capsule of its own. 



The Capsule is a close-fitting, firm, transparent membrane, which is 

 four or five times thicker on the fi'ont than on the back of the lens. 

 The anterior surface of the capsule forms the posterior boundary of the 

 cavity in which the aqueous humom- is contained, and the iris in its 

 movements glides on it. At its periphery the suspensory ligament of 

 the lens blends with it. The posterior surface is in contact with the 

 vitreous humour. 



The lens is a transparent solid body of a biconvex shape, the convexity 

 of its posterior surface being considerably greater than that of ' the 

 antei'ior. It is maintained in a depression on the front of the vitreous 

 humour by a suspensory ligament. This ligament, which is also known 

 as the zonula of Zinn, arises behind and beneath the ciliary processes, 

 where it is connected with the hyaloid membrane of the vitreous 



