58 DR KNOX on the Comparative Anatomy of the Eye. 



ary body and uvea *. It appears, at first sight, a very mechani- 

 cal notion, that the ciliary folds and processes are in a great mea- 

 sure formed, by a membrane being made to occupy a circle na- 

 turally too small for it in its expanded state ; but the way in 

 which these folds commence on the inner surface of the choroid, 

 actually bears out this idea, for the membrane may be unfolded 

 to a very great extent, and thus made to cover a much larger 

 surface. The same remark is applicable to the internal ciliary 

 folds or processes f. The external, or true ciliary processes, 

 have been admirably described and pourtrayed by ZINN, and 

 are, indeed, too well known to all anatomists, to require any par- 

 ticular notice here. Near their base, and between their inter- 

 vals, they are firmly fixed to the capsule, covering the canal of 

 Petit by a mechanism which I shall now endeavour to describe. 

 It has always been asserted, that when the ciliary processes are 

 removed from the humours, their impressions only remain ; but 

 this is incorrect. I at first thought that a portion of their sub- 

 stance was left adhering to the capsule over the canal of Petit ; 

 but further, and a more careful examination, proved this opinion 

 to be erroneous. When the iris is drawn backwards, after ha- 

 ving removed the cornea, and allowed the aqueous humour to 

 escape, the anterior edge of the ciliary processes may be seen 

 projecting into the posterior chamber of the aqueous humour ; 

 and on drawing these also backwards, a number of parallel fibres 

 are seen proceeding from the marginal or equatorial edge of the 

 capsule of the lens, to be inserted between each of the ciliary 

 processes. These fibres lie immediately over the canal of Petit, 

 and contribute with the perfectly transparent membrane lying 



* Some anatomists have confined their description of the uvea to the coating of 

 the pigmentum nigrum, found on the posterior surface of the iris ; but this is not ge- 

 nerally received. 



f These are described a little below. 



