266 ELEMENTAEY PHYSIOLOGY. [XXVI. 



incisions at right angles to one another on the 

 surface of the lens, it will be seen that the lens 

 is covered by a membrane ; this is the anterior 

 part of the lens capsule. Carefully remove 

 the lenSj'^and trace out the limits of the lens 

 capsule, noting that it forms a complete in- 

 vestment for the lens. 



11. Gently separate with the handle of a scalpel the 

 lens capsule from the front part of the ciliary 

 processes, and observe that a membrane, the 

 suspensory ligament or zone of Zinn, passes 

 from the edge of the capsule to the ciliary pro- 

 cesses, of which it forms the innermost layer, 

 dipping , down into their depressions. Poste- 

 riorly it is continuous with the thin hyaloid' 

 membrane (cp. § 9). 



12. Looking into the eye from the front, observe 



a. The entrance of the optic nerve. 



h. The blood-vessels running in the retina and 

 radiating out from the entrance of the optic 

 nerve, 



c. The iridescence, mainly below the entrance of 

 the optic nerve ; it is caused by the irregular 

 reflection of light from the wavy connective- 

 tissue fibres of the choroid. In this region 

 (the tapetum) the hexagonal cells of the 

 retina have no pigment. 



13. Separate the rest of the retina from the choroid, 

 and observe that 



