Sir Everard Home on the anatomical structure, &c. 77 
Between these membranous processes there are bundles of 
muscular fibres of of an inch in length, which I believe 
have not before been described : they originate all round 
from the capsule of the vitreous humor, pass forward over 
the edge of the lens, are attached firmly to its capsule and 
there terminate, as is seen in the drawings. They are un- 
connected with the ciliary processes, or iris. In the human 
eye, and that of the quadruped, they form bundles with inter- 
mediate spaces. In the bird, they are nearly one continued 
layer of muscular fibres. The choroid coat, which may be 
said to terminate anteriorly at the ciliary processes, is mem- 
branous in its structure ; so far similar to the marsupium of 
the bird when unfolded ; but in the choroid coat, Mr. Bauer 
has discovered lymphatic vessels, one on each side of every 
principal artery, not before ascertained, although there could 
be no doubt of their existence; and the arteries, as will be 
seen in the drawings, have not the usual direction, but run 
parallel to one another, totally unlike those in the marsupium. 
In the quadrupeds with the tapetum lucidum, the nigrum 
pigmentum is principally deposited between the sclerotic and 
choroid coat. In the human eye and that of the bird, be- 
tween the choroid coat and retina, a thin pellucid covering 
being interposed between it and the expansion of the optic 
nerve ; the marsupium has a similar covering between the 
nigrum pigmentum and the vitreous humor. The colour 
of the nigrum pigmentum differs in intensity according to the 
colour of the hair; and when the animal is quite white, ap- 
pears to be altogether wanting. That the marsupial mem- 
brane secretes the nigrum pigmentum, there can be no doubt ; 
and for that purpose it is very abundantly supplied with large 
