of the Canal of PETIT. 243 



lentis et corporis vitrei quae elegantissimum spectaculum quod 

 nunquam satis verbis efferri potest, oculis exhibent." 



Again, speaking of the veins of the choroid, he says, " Pau- 

 latim magis parallels fiunt, minutissimae hae venulaa si accesse- 

 rint ad posteriorem terminum processuura ciliarium, ubi retina 

 crassiori sua parte, ad limbum posteriorem corporis ciliaris adhae- 

 rescit, et ubi retina subtilissimam lamellam emittit, quae ut sub- 

 tilissimum velamentum annulo mucoso, subjectam ad ambitum 

 capsulae , lentis advenit, et ubi ea in convexitatem anteriorem 

 transire incipit, huic adhasret." And a few pages further on he 

 says, " Ex hoc reti admirabili ciliari, ubi illud apicem processu- 

 ura ciliarium operit, exeunt minutissimi surcuh' qui subtilissimam 

 productionem retinae antea descriptam perforant, et paululum re- 

 flectendo, adeunt membranam corporis vitrei annulo mucoso 

 tinctam, plurimi horum surculorum se immergunt in capsulam 

 lentis, ubi ea, ope laminae anterioris zonula? ciliaris ZINNII, fir- 

 miter cum hyaloidea cohaeret, qui profundius delati in posteriore 

 convexitate capsulae lentis terminantur." 



I do not hesitate in ascribing to these processes, or at least 

 to the vessels distributed to them, the office of secreting the vi- 

 treous humor, of restoring it when partially lost, a process 

 we know to be very limited, and of absorbing, by means of pro- 

 per vessels, the superfluous parts *. In birds, we find that the 

 inner membrane of the retina is no longer vascular, and, in- 

 deed, is with difficulty demonstrated. I have not been able to 



* It seems unnecessary to remark, that the secretion must ultimately be effected 

 by means of vessels carrying colourless fluids, proceeding from those of a larger ca- 

 liber, and distributed on the parietes of the canal of Petit. Vessels carrying co- 

 lourless fluids no doubt penetrate into every part of the vitreous humor. Physiolo- 

 gists are as yet but little acquainted with the nature of the vessels carrying colourless 

 fluids only. 



