72 DR KNOX on the Comparative Anatomy of the Eye. 



We shall discuss, whilst considering the ciliary nerves, the 

 long agitated question, Whether the iris be a voluntary or invo- 

 luntary muscle. On the death of an animal, the pupil is in ge- 

 neral much dilated, but it again contracts whilst the other 

 muscles of the body are becoming rigid, these phenomena being 

 analogous. I have fancied that, in the horse, some time after 

 death, the pupil is more contracted than in most animals, which 

 may be attributed to the superiority of the sphincter over the 

 dilating part of the iris, and this is probably connected with the 

 peculiar fringe in which the superior margin of the pupil termi- 

 nates, compared not unaptly by SWAMMERDAM to the fringed 

 curtain-like body in which a part of the pupillary margin in the 

 eye of the skate terminates. There is a similar appearance, 

 though not fringed, nor yet so distinct, in the eye of the com- 

 mon dolphin. 



III. Of the Ciliary Nerves, their Nature, and Distribution. 



I regret that it will not be in my power to enter into any very 

 lengthened details relative to the ciliary nerves, and that I shall 

 be necessitated (by other avocations) to limit myself to a mere 

 outline, drawn up hastily, and even carelessly, though from nu- 

 merous dissections. 



The nerves supplying the iris and ciliary muscle are derived 

 from the third and fifth pairs of cerebral nerves. They generally 

 form a ganglion, previous to giving off the true ciliary nerves ; 

 which ganglion is sometimes wanting, and would seem to have 

 but little influence over the action of the nerves. It resembles 

 anatomically, and perhaps physiologically, the gangh'on formed 



