62 DR KNOX on the Comparative Anatomy of the Eye. 



By means of these transparent membranes, which I have called 

 the Internal Ciliary Processes, (or the ciliary processes of the 

 hyaloid membrane), the vitreous humour and lens are intimately 

 united together ; but it is also, as I have already shewn, by 

 means of the same membrane and processes that the humours of 

 the eye are affixed to the tunics immediately connected with 

 them, viz. the external ciliary processes, ciliary muscle, sclerotic, 

 &c. ; for the internal ciliary processes pass in between the folds 

 of the great or external ones, throughout a great part of their 

 course, and anteriorly near their termination in the capsule of 

 the lens, they send up numerous processes, to be inserted into 

 the superincumbent ciliary body between each of the ciliary pro- 

 cesses. Some have supposed these reduplications of the mem- 

 brane to be muscular fibres, an opinion against which we have 

 both ocular inspection and analogy. I am not prepared to as- 

 sert that microscopic fibres do not exist, but these, from their 

 very nature, must be exceedingly unimportant. 



Of the Pigmentum Nigrum and its Membrane. 



The late Dr MONRO observed, in two cases, a membrane 

 shutting up the pupil, the result of inflammation ; and in both 

 the posterior surface of the membrane was coated with pigmen- 

 tum nigrum. From this, and some other observations, I am in- 

 clined to think, that the pigmentum nigrum, in many animals, is 

 inclosed in a peculiar membrane, and that this membrane may 

 be continuous with that lying immediately external to the reti- 

 na, and betwixt it and the choroid coat, and generally known by 

 the name of the Membrane of Jacob. It is true, that through- 

 out a great part of its course, this membrane, when present, is 

 semitransparent, and that which sometimes incloses the pigmen- 

 tum nigrum is dark and opaque ; but I hare already demon- 



