of the Canal of PE TI T. 247 



internal ciliary processes commence, and where the pulpy por- 

 tion of the retina ceases, there is detached a delicate colourless 

 membrane over the whole anterior concave surface of the vitre- 

 ous humor, and which, as is very correctly stated in anatomical 

 works, is merely contiguous to the posterior surface of the cap- 

 sule of the lens, but is not in any way connected with it. This 

 contiguity I perceived to be constant, by reason, probably, of the 

 elasticity of the membranes I am next to describe, viz. those im- 

 mediately forming the canal of Petit. 



After the layer of the hyaloid membrane which invests the 

 anterior aspect of the vitreous humor has been detached, the 

 remaining structure passes on towards the equatorial margin of 

 the lens; but, previous to being fixed into its capsule, it al- 

 ters very much in appearance, and assumes a structure I have 

 already often described. It divides into two distinct layers ; the 

 external or outer, constituting the internal ciliary processes, and 

 an inner membrane, also vascular, separating the canal of Petit 

 from a cavity, which may be formed artificially, by blowing in air 

 betwixt the posterior surface of the capsule of the lens, and the 

 hyaloid membrane on which this rests *. Just as the membranes 

 forming the canal of Petit are about to reunite, they adhere 

 firmly to the capsule of the lens, and seem to transmit another 

 very delicate membrane, closely investing the posterior surface 

 of that capsule. This is the whole mechanism of the canal f . 



* Marked h on the accompanying figure. 



f 1 should think Mr JACOBSON in error, with regard to the openings he supposed 

 he discovered in the canal of Petit. The membrane passing betwixt the internal cilia- 

 ry processes, or its outer paries, is excessively delicate, and may possibly have been 

 ruptured. On this subject HALLEE expresses himself very positively, and with 

 much accuracy and brevity : " Flatu enim immisso adparet circulum Petit solum 

 inflari, neque aerem aut in lentem subire, aut in vitreum corpus, eum ergo circulum 

 VOL. X. P. II. I i 



