Section 2. 

 Smell. 



The Olfactory Organ. — The nasal chambers are divided by a 

 septum, and each chamber contains the turbinated bones. It 

 has been observed that acuteness of smell is often associated 

 with large and extremely convoluted turbinates. By the 

 position of these bones the nasal passage may be divided into 

 two channels, one which lies next the floor of the chamber, 

 which, from its obvious communication leads directly to the 

 respiratory passages, and another channel which lies above it 

 and leads to structures situated very high in the face and nose. 

 One is known as the respiratory and the other the olfactory 

 passage. But apart from this there are differences in the 

 physical characters of the mucous membrane of the nasal 

 chambers ; that of the olfactory region differs from the respiratory 

 portion in being thicker and of a yellowish tint, and it is in this 

 membrane that the fibres of the olfactory nerve are distributed. 

 Both the respiratory and olfactory portions of the nasal chambers 

 are supplied with sensation by the fifth pair of nerves. In the 

 horse the nasal chambers are of extreme importance, inasmuch 

 as he is the only animal we are called upon to deal with which 

 is unable to breathe through the mouth ; the majority of animals 

 can breathe through both nose and mouth, but owing to the 

 extreme length of the soft palate in the horse this is under 

 ordinary circumstances impossible. So far as respiration is 

 concerned the question of the nostrils has been dealt with (p. 115) ^ 

 but the arrangement of that portion devoted to the sense of 

 smell has yet to be considered. 



Olfactory Nervous Mechanism. — From the olfactory tracts in 

 the brain the olfactory lobes are formed, which in some animals 

 possess a well-marked cavity, in others only a canal. In the 

 cavity some fluid is contained which communicates with the 

 cerebro-spinal, and notably in the horse with that contained in the 

 lateral ventricles. From the large olfactory bulbs non-medullated 

 nerve fibres are given off, which penetrate the cribriform plate 

 of the ethmoid, and ramify over the mucous membrane, covering 

 the upper portion of the septum, the superior turbinated bone, 

 and the upper third of the superior and middle meatus. 



These nerve fibres terminate in olfactory sense organs, which 

 are specialised nerve cells, from the free end of which project a 

 tuft of hair-like processes, which are acted upon by olfactory 



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