a membrane in the eye. 305 
contact, they are connected to each other by cellular sub- 
stance, and, consequently, by vessels ; for I consider the failure 
of injections no proof of the want of vascularity in transpa- 
rent and delicate parts, though some anatomists lay it down 
as a criterion. Undoubtedly 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 scissors through the choroid coat into the vitre- 
ous humor, 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 does not recede from the 
membrane I describe, the membrane from the retina, nor the 
retina from the vitreous humor. I take the end of the por- 
tion of choroid 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 connection. I separate the membrane in like 
manner, but the retina I can scarcely detach from the vitreous 
humor, so strong is the connection. The same fact may be 
ascertained by making a transverse vertical section of the 
eye, removing the vitreous humor from the posterior seg- 
ment, and taking the retina in the forceps, pulling it gently 
from the choroid, when it will appear beyond a doubt that 
there is a connection between them. 
Let us contrast this account of the matter with the com- 
mon one. The retina, a membrane of such delicacy, is 
mdcccxix. R r 
