130 Aciounl of a Membrane in the Eye 



though smali portioijs are sometitnesi pulled off with the choroid 

 coat. From this fact I think it follows, that the accounts hitherto 

 given of the anatomy of these parts are incorrect. The best ana- 

 tomists* describe the external surface of the retina as being 

 merely iu contact with the choroid coat, as the internal with the 

 vitreous humour, but both totally unconnected bv cellular mem- 

 brane, or vessels, and even having a fluid secreted between them: 

 some indeed speak loosely and generally of vessels passing from 

 the choroid to the retina; but obviously not from actual observa- 

 tion, as I believe no one has ever seen vessels passing from the 

 one membrane to the other. Mv observations lead me to con- 

 clude, that wherever the different parts of the eye are in contact, 

 they are connected to each other by cellular substance, and, con- 

 sequently, by vessels ; for I consider the failure of injections no 

 proof of the want of vascularity in transparent and delicate parts, 

 though some anatomists lay it down as a criterion. UndoubtedK 

 the connection between these parts is exceedingly delicate, and, 

 hence, is destroyed by the common method of examining this 

 organ ; but I think it is proved in the following way. I have 

 before me the eye of a sheep killed this day, the cornea secured 

 to a piece of wax fastened under water, and the posterior half of 

 the sclerotic coat carefully removed. I thrust the point of the 

 blade of a pair of sharp scissars through the choroid coat into the 

 vitreous humour, to the depth of about an eighth of an inch, 

 and divide all, so as to insulate a square portion of each mem- 

 brane, leaving the edges free, and consequently no connection 

 except by surface; yet the choroid doe? not recede from the mem- 

 brane I describe, the menilnane from the retina, nor the retina 

 from the vitreous humour. ! take the end of the portion of cho- 

 roid in the forceps, turn it half down, and pass a pin through the 

 edge, the weight of which is insufficient to pull it from its con- 

 nection. I separate the membrane in like manner, but the re- 

 tiiia I can scarcely detach from the vitreous humour, so strong 

 is. the connection. The same fact maybe ascertained by making a 

 transverse vertical section of the eye, removing the vitreous hu- 

 mour from the posterior segment, and taking the retina in the 

 forceps, pulling it gently from the choroid, when it will appear 

 beyond a doubt that there is a connectioii between them. 



Let us contrast this account of the matter with the cominon 

 one. The retina, a membrane of such delicacy, is described «s 

 being extended between the vitreous hucnour and choroid, from 

 the optic nerve to the ciliary processes, being merely laid betwec-s) 



* See Haller, Elem. Phys. t. v. lib. xvi. sect. ii. Zinn. cap. ii. sect. i. § ii. 

 Boyer, Anat. t. iv. p. 1 13. Sabaticr, t. ii. p. 70. Bichat, Anat. Descr. t. ii. 

 p. 447. Cuvier, Le^^ons d'Anat. Comp. t. ii. p. 418. Charles Bell, Anat. 

 Toi. iiL p. 51. Ribss, Meiu. de la Scu. Aled. d Emulation, t. viii. p. 633. 



them, 



