444 THE HORS. 
CHAPTER XXIV. 
SPECIAL ORGANS. 
THE ORGAN OF SMELL—THE EYE—THE EAR—THE ORGAN OF TOUCH—THE FOOT. 
THE ORGAN OF SMELL. 
Tur nose of the horse, like all the solipedes, is endowed with a sep. 
sibility far greater than that of man ; but in this respect he is not equal 
to many other animals, such as the dog and cat kinds, and the sole use 
which he makes of this sense is in the selection of his food. I have 
already alluded to the nasal fossee at page 419, and need only here remark 
that the large mass of nervous matter composing the olfactory nerves 
pierces the cribriform plate of the «thmoid bone in numerous fibrille, 
which spread over the membrane (Schneiderian) lining the «thmoidal 
cells, the turbinated bones, and the septum nasi. 
THE EYE. 
THE ORGAN OF SIGHT may be considered as consisting, first of all, of an 
optical instrument very similar to the camera obscura, now so commonly 
used in photography, and, secondly, of the parts which are employed to 
move, adjust, and protect it from injury. 
Tur EYE itself consists of three transparent humours, which answer 
the purpose of the lens of the camera, by collecting the rays of light 
upon the back of the eye. These are the aqueous in front, the crystalline 
lens in the middle, and the vitreous humour behind. The first is a per- 
fectly transparent and limpid fluid, secreted by the lining of the chamber 
in which it lies, and capable of being rapidly renewed in case of a punc- 
ture letting it out. The lens, on the contrary, has the consistence of very 
hard jelly, and is arranged in concentric layers, like the coats of an onion. 
It is merely a double convex lens, precisely like that of the camera, in its 
action, and is the chief agent in producing the impression of an object 
upon the sensitive part of the eye. Behind it is the vitreous humour, 
composed, like the abueous, of a limpid fluid ; but instead of being uncon- 
fined except by the walls of the chamber in which it hes, it is bound up 
in a network of transparent cells, which give it the consistency and 
appearance of a delicate jelly. Upon the perfect transparency and proper 
shape of these humours depends the sight of the animal. But in addi- 
tion to the risk of blindness from any defect in these parts, if the 
investing coats or membranes are inflamed or disorganised, their func- 
tions are not performed, and the sight is either impaired or destroyed. 
Thus the rays of light may be fairly collected, so as to throw the impres- 
sion of every object within the sphere of vision upon the back of the 
eye, and yet the horse may be blind, because the retina or expansion 
of the optic nerve is disorganised by disease. When inflammation 
attacks the coats of the eye, it generally extends to the investments of 
the humours, and to the substance of the lens itself, producing cataract 
or opacity of that part; but it is possible to have the sight impaired 
from a mere defect of shape in the anterior coat, so as to make the 
