478 Dynamic Theory. 



tubes which open into the moum cavity are gradually carried further 

 j:< .vard, a process which necessarily leaves a constantly increasing plate 

 or partition between the mouth and the nasal cavities. This separating 

 plate is the palate or roof of the mouth ; the nasal cavities opening be- 

 hind it into the back part of the mouth, and lastly behind the mouth in- 

 to the pharynx. The different stages of this progressive movement of 

 the inner ends of the nasal cavities successively represent arrested and 

 stationary conditions in the amphibia, the reptiles, the early mammals, 

 and the higher mammals, in the order in which they are here named, at- 

 taining their complete development in the higher apes and man. The 

 sense of smell in man is less highly developed than in many lower ani- 

 mals, and appears to have become, to some extent, reduced and rudi- 

 mentaiy. In most lower vertebrates, the olfactory lobes are much larger 

 in proportion to the rest of the brain than in adult man, and this same 

 is true of the human foetus. The sensative surface of the pituitary 

 membrane is in man much smaller than the whole membrane. The 

 large amount of functionless surface in the inner nasal cavities would 

 seem to indicate that the habits of the animal ancestors of the race dif- 

 ferentiated and handed down to us a larger olfactory apparatus than we 

 at present use. The acuteness of the sense can be vastly increased in 

 anj^one by persistent habit, and, in all probability, if there were any 

 occasion for it, the race could, by use, become as acute in the sense as 

 dogs and other higher mammals. It is recorded that persons have be- 

 come sufficiently sensitive to recognize other persons by their smell, and 

 in one case a person could pick out his own clothes from among many 

 others by this sense. (Neil & Smith.) 



The eccentricities of the sense are remarkable. One man was insen- 

 sible to all odors except that of a manure heap or rotten cabbage ; an- 

 other could not perceive any smell to vanilla ; another could not perceive 

 the scent of mignonette. The effects of odors on different persons are 

 likewise very different. The scent of apples and roses have been known 

 to be very disagreeable to some persons. Others, again, are pleased 

 with assafretida, valerian-root, the scent of old books, or the smell of a 

 dunghill ( Papillon ). Some people like the odor of musk, which others 

 detest. Many odors are agreeable or beneficial in a small amount which 

 are hurtful or disagreeable when very strong ; and habit often reconciles 

 the sense to what is at first almost intolerable. Plabit, or use, is indeed 

 responsible for every modification of the sense of whatever kind. There 

 is, in fact, the same sort of differen-tation of the epithelial cells into 

 sensitive organs in this case, that we find in the retina of the eye and 

 the crista acustica and scala media of the ear. The modified cells and 

 "rodlike fillaments " of the pituitary membrane are the peers of the 

 11 rods and cones " of the eye, and the arches of Corti, and the auditory 



