Mr. Home's Lecture 
16 
attached to the posterior edge of the bony rim just described : 
they are four in number. 
The ciliary processes are larger and longer in birds, than 
in other animals whose eyes are of the same size ; they are 
evidently continued from the choroide coat, and adhere firmly 
to the capsula of the crystalline lens. 
In the eyes of birds there is a substance which is peculiar to 
that class of animals, called the marsupium. It is a process 
composed of a corrugated vascular membrane attached to the 
centre of the retina, where the optic nerve terminates. Its ori- 
gin is in a straight line, extending from the termination of the 
optic nerve to the lower part of the eye ; in the turkey of an 
inch in length, and connected with the bottom of the eye by 
an elastic ligament about ^ of an inch thick. The number 
of folds of which it is composed varies in different birds, from 
5 to 15, or more ; they are all of the same length, which in 
the turkey is about of an inch ; they are covered with the 
nigrum pigmentum, and are attached anteriorly to the capsula 
of the crystalline lens, either immediately, as in the goose, or 
by intermediate membrane, as in the turkey.* 
The structure of the marsupium is very similar to that of 
the ciliary processes, but stronger in all its parts, and like them 
it has a connection with the crystalline lens. 
The connection between the marsupium and lens, in a 
natural state of the parts, is from its transparency invisible ; 
but in the goose and cassuary, where the marsupium extends 
to the capsula of the lens, if the parts are coagulated in spirits, 
it becomes very apparent, and in these birds such a connection 
is generally allowed. In other birds, it is doubted by some, and 
* Vide plate. 
