496 THE ANATOMY OF THE HOUSE 



CnAPTEU XXIV 



SPECIAL 0Ri;AX3 



THE onnAN of smei.l— the kye— the ear— the organ of tovcu— the foot 



THE ORGAN OF SMELL 



TnE NOSE of tlio liorso, like all the soiipedcs, is endowed with a sensibility 

 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 fossae at page 469, and need only here remark that the large 

 mass of nervous matter composing the olfactory nerves pierces the cribriform 

 plate of the aHhmoid bone in numerous fibrilUv, which spread over the 

 membrane (Schneiderian) lining the tethmoidal cells, the turbinated bones, 

 and the septum nasi. 



THE EYE 



TiiF. orgav of siciit may be considci'cd as consisting, first of all, of an 

 optical instrument very similar to the camera obscura, now so commonly 

 used in photography, and, secondl}", of the parts which are employed to 

 move, adjust, and protect it from injury. 



The 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. There are the aqueous in front, the crystalline lens in the 

 middle, and the vitreous humour behind. The first is a perfectly trans- 

 parent and limpid iluid, secreted by the lining of the chamber in which it 

 lies, and capable of being rapidly renewed in case of a puncture 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 aqueous of a limpid fiuid ; but instead of being unconfined except by 

 the walls of the chamber in which it lies, 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 addition to the risk of 

 blindness from any defect in these parts, if the investing coats or membranes 

 are inflamed or disorganized, their functions 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 impression of every object within the sphei'e 

 c£ vision upon the back of the eye, and yet the horse may be blind, becausu 



