OF THE SENSE OF SIGHT. 119 



passing through the sclerotic and choroid, and terminates in 

 the retina, which is generally viewed as an expansion of this 

 nerve. But other nerves 

 enter the eyeball, such as 

 the ciliary, coming partly 

 from the fifth pair and 

 partly from a ganglion, the 

 ophthalmic, with which the 

 fifth and third communi- 

 cate. From this ganglion, 

 though small, most of the 

 ciliary nerves proceed into 

 the interior of the eye to 

 supply the ciliary circle and 

 the iris. ' r v pc b 



m The ciliary ligament or rig> 76> _ Globe of the Eye 



circle is a peculiar ring con- Dissected.* 



necting the choroid, iris, 



and sclerotic to each other. Its nature and functions have 

 not yet been determined, but it is well supplied with nerves 

 in animals of strong vision, as in the eagle and vulture. 



[An extended series of inquiries into the structure of the 

 ciliary ligament, or body, induced me, many years ago, to believe 

 it to be of the same structure as the iris, and to assign to it the 

 functions of the adaptation of the eye to various distances. See 

 "Trans. Roy. Soc. of Bdin.," 1827. R. K.] 



The humours are colourless and transparent, and the same 

 remark applies to all the parts situated between the exterior 

 and the retina in the axis of vision, or measured by the size 

 of the pupil. The cornea is everywhere absolutely trans- 

 parent, and so is the conjunctiva which covers it. 



In the iris, some of the fibres proceed like radii from 

 the free edge of the pupil towards the base : others surround, 

 as it were, the pupil, and act like a sphincter in contracting 

 the orifice. The aqueous humour, though quite transparent, 



* c, the transparent cornea; s, sclerotic ; s', portion of the sclerotic turned 

 back to display portions of the membranes situated beneath it ; ch, the cho- 

 roid ; v t the retina ; n, the optic nerve ; ca, anterior chamber of the eye, 

 situated between the cornea and the iris, and communicating with the pos- 

 terior chamber by the opening in the iris called the pupil ; these chambers 

 contain the aqueous humour ; *, the iris ; p, the pupil, an opening in the iris 

 by which the rays of light pass into the deeper chambers of the eye ; cr, the 

 crystalline humour or lens ; pc, ciliary processes ; v, vitreous humour ; 

 b b, & portion of the conjunctiva. 



