236 DR KNOX on the Philosophical Anatomy 



expressed in my former paper on the Comparative Anatomy of 

 the Eye. I therein state, that the pulpy layer of the retina 

 terminates by a well-defined margin near to the place where the 

 internal ciliary processes (Zonula Ciliaris of ZINN) commence ; 

 but that the inner layer of the retina may be considered as ad- 

 vancing forwards towards the lens, and uniting with the other 

 transparent tunics to form the internal ciliary processes *, and 

 the internal parietes of the Canal of Petit. I still admit, that this 

 opinion rests partly on analogy, but on analogy of the strongest 

 nature. We see the inner tunic advance forwards to the point 

 where the internal ciliary processes commence ; from this point 

 forwards to the capsule of the lens, the structure has changed 

 considerably ; the membrane has become much more vascular, 

 and it is folded into numerous plaits : but the difference in struc- 

 ture is not greater than what takes place in the corresponding 

 coloured membranes ; viz. the choroid and true ciliary processes ; 

 and I hold the analogy as to form, structure, and relation to 

 their respective membranes, as complete. The fact that the 

 retina separates very readily (after a little maceration) from the 

 portion of the vascular tunic, which we may suppose as contri- 

 buting to form the internal ciliary processes, merely shews, that, 

 at this part, the membrane is very delicate, and easily torn, but 

 perhaps not more so than at any other point of the retina. 



This question was much disputed in HALLER'S time : he 

 adopted the opinion, that the inner or vascular tunic of the reti- 

 na extends as far as the capsule of the lens ; he even shewed 



* These internal ciliary processes were called Fibres by ZINN, Lymphatic Vessels 

 by BERTRANDI, and Tendinous Fibres by CAMPER. They are composed chiefly of 

 arteries and veins. TENON well understood their anatomy, and describes their mode 

 of union with the true ciliary processes, and the important fact of their receiving 

 bloodvessels from the latter organs. 







