248 DR KNOX on the Philosophical Anatomy 



II. Of the Membrane of JACOB. 



WE owe to the excellent anatomist whose name this mem- 

 brane bears, the first correct description of a most interesting 

 texture of the eye-ball, which had been talked of before his day 



versus lentem capsula claudi. Deinde sola lentis capsula facile inflatur, neque aer 

 aut in circulum, aut in vitreum transit. Denique etiam vitreum corpus aerem reci- 

 pit, qui neque in lentem transit, neque in Petit annulum." 



HALLER'S description of the canal of Petit is obviously incorrect ; and Mr CLO- 

 QUET, by copying this description, but superadding to it the well ascertained fact, 

 that the layer of the hyaloid membrane covering the anterior aspect of the vitreous 

 humor, that, viz. upon which the lens with its capsule reposes, does not adhere to 

 the capsule, has become thereby quite unintelligible. I here quote both passages. 



" Lamina posterior vitreae membranse discedit ad originem processuum ciliorium, 

 et ad lentem introrsum etiam, sed paulo posterius advenit, recta protensa, et earn 

 porro postquam attigit, tenaciter satis conjuncta, posterius includit. 



" Inter has duas teneras laminas flatus potest immitti, qui circularem canalem, fre- 

 nulis subinde adstrictum, efficit," &c. But I have shewn, that if a delicate mem- 

 brane be actually stretched over the posterior surface of the capsule of the lens, nei- 

 ther this lamina, nor that placed immediately behind it, inclosing the vitreous humor 

 have any thing to do with the formation of the canal of Petit. 



The passage alluded to in Mr CLOQUET'S work is as follows : " Au niveau des 

 proces ciliaires, vers le contour du crystallin, cette membrane (hyaloide) se divise 

 en deux lames ; Tune passe devant la capsule de ce corps, et Tautre tapisse la conca- 

 vite qui le re9oit en arriere. II result de leur ecartement un espace de la forme d'un 

 prisme circulaire a trois pans, complete par le circonference du crystallin. C'est cet 

 espace vide qu'on appele Canal Godronne ou Goudronna, ou Canal de Petit." 



HAULER says that the canal of Petit is present in all quadrupeds ; an observa- 

 tion which agrees with the almost innumerable dissections I have made of that 

 organ. He thinks it totally wanting in birds : I have proved that the only important 

 part entering into its composition, viz. its vascular part, is wanting in these animals 

 for this very obvious reason, that its place is supplied by the marsupium ; but it 

 seems to me that there still exists, as it were, a rudiment of the part, though by no 

 means distinct. 



