170 
Mr. Bell on the motions of the eye , &c. 
preservation of the eye, in the manner in which the eye-lids 
close, which has not been noticed ; while the upper eye-lid 
falls, the lower eye-lid is moved towards the nose. This is 
a part of that curious provision for collecting offensive par- 
ticles towards the inner corner of the eye. If the edges of 
the eye-lids be marked with black spots, it will be seen that 
when the eye-lids are opened and closed, the spot on the 
upper eye-lid will descend and rise perpendicularly, while 
the spot on the lower eye-lid will play horizontally like a 
shuttle. 
To comprehend certain actions of the muscles of the eye, 
we must remember that the caruncle and membrane called 
semilunaris, seated in the inner corner of the eye, are for 
ridding the eye of extraneous matter, and are in fact, for 
the same purpose with that apparatus which is more perfect 
and appropriate in beasts and birds. 
The course of our enquiry makes some observation of 
these parts necessary. 
In quadrupeds there is a gland for secreting a glutinous 
and adhesive fluid, which is seated on that side of the orbit 
next the nose ; it is quite distinct from the lacrymal gland ; 
it is squeezed by an apparatus of muscles, and the fluid 
exudes upon the surface of the third eye-lid. This third 
eye-lid is a very peculiar part of the apparatus of preserva- 
tion. It is a thin cartilage, the posterior part of which is 
attached to an elastic body. This body is lodged in a divi- 
sion or depression of the orbit on the side towards the nose. 
When the eye is excited, the eye-ball is made to press on the 
elastic body and force it out of its recess or socket ; the con- 
sequence of which is the protrusion of the cartilaginous 
