DR KKOX on the Comparative Anatomy of the Eye. 63 



trated, that this happens with the reflected membranes of the 

 choroid, and with several other membranous tissues of the eye. 

 In this case we should consider the membrana Jacobi as extend- 

 ing to the very edge of the pupil. The appearances, in the eye 

 of the cassowary, and in fishes, prove that there does exist a 

 membrane in the situation described. 



The anatomy of the fishes' eye, which I shall now very brief- 

 ly describe, supports these opinions. Though a few striae may be 

 observed on the inner surface of the choroid in fishes, yet they 

 cannot be considered as constituting a ciliary body, whilst it is 

 very evident that there are no ciliary processes. The attach- 

 ment between the choroid and humours is by no means firm, but 

 still it exists, and the mode is as follows : On tearing off the scle- 

 rotic and cornea, a greyish-white line or chord, of considerable 

 thickness, is left. The choroid evidently passes under it, to in- 

 vest the internal surface of the transparent iris * ; but they can- 

 not be easily separated from each other. The proper choroid, 

 and innermost layer of this compound membrane, which had 

 been separated from each other posteriorly by the choroid gland, 

 unite intimately where the retina terminates, to pass forward 

 beneath the iris. A dark coloured fluid pigment covers the 

 whole surface of the retina, separated from it, however, by a thin 

 membrane ; but from the termination of the retina forwards, to 

 the very edge of the pupil, this pigment assumes the form of a 

 striated close membrane, perfectly black, and much resembling 

 the ciliary folds in the mammalia, and even possessing, as in the 

 cod, a beautiful fringed border, by which it adheres to the cap- 

 sule of the vitreous humour. In other words, the pigmentum 

 nigrum is no longer deposited on the surface of the choroid, but 



* i. e. Supposing an iris to exist betwixt the prolongation of the choroid and 

 the reflected membrane of the cornea, which I do not believe to be the case. 



