Da KNOX on the Comparative Anatomy of the Eye. 51 



of a person actually dead. We have, moreover, seen many in- 

 stances, in which the cornea retained its fullness and lustre for 

 some time after death had taken place. These various effects 

 are attributable to the different degrees of energy remaining in 

 the external muscles of the eye-ball. After a time, a film forms 

 on the surface of the cornea. I have already stated, that the an- 

 terior layer of the iris is inserted into the inner membrane of the 

 cornea, and that this forms a principal attachment. If the ana- 

 tomy of the eye in fishes be considered as affording a fair analo- 

 gy, we are warranted in asserting, that the inner membrane of 

 the cornea covers the whole anterior surface of the iris, though 

 the ox, the deer, and some other animals, present the modifica- 

 tion before described. On this depends the elasticity of the iris 

 in birds ; and, in fishes, we are compelled to admit this continui- 

 ty of the membranes ; for, between the coloured portion of the 

 iris, which, in them, we know to be the external layer of the 

 choroid, and the aqueous humour of the anterior chamber, there 

 exists no other membrane, than a thin, transparent, elastic tunic, 

 continuous with, and exactly resembling, the inner layer of the 

 cornea. We cannot well doubt that the action of the iris on this 

 membrane must alter, to a certain degree, the form of the cor- 

 nea internally, and, consequently, that of the aqueous humour, 

 which opinion was long ago maintained by JURIN, and admits al- 

 most of demonstration. 



II. Of the Choroides, and its Appendages ; of the Iris and its 

 Motions ; of the entry of the Optic Nerve into the Eye ; and 

 of the Distribution of the Ciliary Nerves. 



WE give the name of Choroides to that dark coloured mem- 

 brane found immediately within the Sclerotic. By Comparative 

 Anatomy, we best learn the nature of this membrane, the num- 



