on Muscular Motion. 
15 
can be produced upon the posterior part of the rim, the diffe- 
rent parts being too firmly connected to admit of any sepa- 
ration. 
The structure of this bony rim differs in different birds. In 
the goose and turkey the scales are thin and weak ; in the 
cassuary they are thicker ; and in the eagle they are very 
strong. In the owl, they put on a very different appearance ; 
they are 15 in number, ^ of an inch long, and instead of be- 
ing lapped over one another, as in other birds, they are united 
by indented sutures ; each portion is broadest next the sclerotic 
coat, and narrowest towards the cornea, giving the bony rim 
a conical form.* 
This structure in the owl’s eye differs from that in other 
birds, the anterior edge not admitting of being dilated to cor- 
respond with the change of figure in the cornea ; this purpose 
in the owl is answered by a circular elastic ligament firmly 
attached to the anterior edge of the bony rim, and lying upon 
the outside of the basis of the cornea ; there is a similar liga- 
ment in other birds, but less conspicuous. 
This bony rim in the eyes of birds is particularly noticed by 
Haller ; specimens of it, whole and in separate parts, are 
preserved in Mr. Hunter’s collection ; it has been also de- 
scribed by Mr. Smith, in a paper read before this Society : I 
shall, therefore, not dwell longer upon its structure, as it is 
not to my present purpose to take further notice of it than to 
explain its use respecting the adjustment of the eye, the sub- 
ject of the present lecture. 
The straight muscles of the eye in birds arise from the 
bottom of the bony orbit 3 as in the quadruped, and are firmly 
* See the annexed plate. 
