Sir Everard Home on the 
78 
arteries. That the choroid in the human eye, as well as that 
of the bird does the same, is in some measure proved by the 
fine injection thrown into the arteries of that membrane escap- 
ing from their termination, so as to form a layer of injection 
behind the retina without the smallest appearance of extra- 
vasation. 
The membrane between the nigrum pigmentum and retina, 
has been described by Dr. Jacob, of Dublin, and his account 
of it published in the Philosophical Transactions. The nigrum 
pigmentum appears to be nothing more than the colouring 
matter of the red globules, rendered black in the act of sepa- 
ration from the arteries ; it is also deposited upon the surface 
of the ciliary processes and iris, by the arteries with which 
they are loaded, and covered by a pellucid membrane. 
In the horse, the arteries of the ciliary processes are very 
large; and I am led to believe that the extraordinary disease 
that animal is liable to in India, of having two species of 
worms (the strongylus armatus and filiaris papillosa) found 
alive in the aqueous humor, is produced by the ova or young 
worms escaping from the terminations of those arteries ; more 
especially as Mr. Hodgson, in his engravings of diseased arte- 
ries, has figured the strongylus armatus adhering to the inner 
membrane of the superior mesenteric artery of the horse, 
showing that in that animal it gets into the circulation. 
The iris is fixed at its origin to the annular ligament; is 
divisible into two layers ; the posterior, muscular ; the fibres 
radiating towards the pupil, at which part there is a regular 
sphincter muscle ; the anterior, membranous. 
My friend Mr. Maunoir, of Geneva, is, I believe, the first 
person who made out this structure, and gave an engraving of 
