THE NERVOUS SYSTEM AND ORGANS OF SENSE. 221 
the cornea. Within this are two unequally-sized chambers 
separated by a vertical curtain, the ats, with a central aperture, 
and by a dense transparent body enclosed in a very delicate mem- 
brane or capsule. This dense, transparent body is the crystalline 
lens,which fills the aperture—the pupil—left in the middle of the 
iris. Around the lens are small processes termed ciliary processes. 
Round the iris is a fibrous band called the ciliary ligament, while 

Sipe View or Mempranous Lasyrinti or Picron: greatly enlarged. 
ca, cp, and ce, anterior, posterior, and external semicircular canals ; 
co, cochlea. 
on the outer surface of the choroid is a similar band of contractile 
fibres—the ciliary muscle. The chamber in front of the lens is 
filled with the aqueous humour, while the vitreous humour fills 
that behind it. Lining this posterior chamber is the essential 
organ of sight, the expanded optic nerve or retina. External to 
this is a dark, highly yascular membrane termed the choroid. 
