•362 ELEMENTARY PHYSIOLOGY less. 



which separates the two nostrils one from the other. 

 Below, each nasal chamber is separated from the cavity of 

 the mouth by a floor, the bony palate (Figs. 115 and 116) ; 

 and when this bony palate comes to an end, the partition 

 is continued down to the root of the tongue by a fleshy 

 curtain, the soft palate, which has been already described. 

 The soft palate and the root of the tongue together, 

 constitute, under ordinary circumstances, a movable 

 partition between the mouth and the pharynx ; and it 

 will be observed that the opening of the larynx, the 

 glottis, lies behind the partition ; so that when the root of 

 the tongue is applied close to the soft palate no passage 

 of air can take place between the mouth and the pharynx. 

 But in the upper part of the pharynx above the jjartition 

 are the two hinder openings of the nasal cavities (which 

 are called the posterior nares) separated by the 

 termination of the septum ; and through these wide 

 openings the air passes, with great readiness, from 

 the nostrils along the lower part of each nasal chamber 

 to the glottis, or in the opposite direction. It is 

 by means of the passages thus freely open to the air 

 that we breathe, as Ave ordinarily do, with the mouth 

 shut. 



Each nasal chamber rises, as a high vault, far above the 

 level of the arch of the posterior nares — in fact, about as 

 high as the depression of the root of the nose. The upper- 

 most and front part of its roof, between the eyes, is 

 formed by a delicate horizontal plate of bone, perforated 

 like a sieve by a great many small holes, and thence 

 called the cribriform plate (Fig. 116, Or.). It is this 

 plate (with the membraneous structures which line its two 

 faces) alone which, in this region, separates the cavity of 

 the nose from that which contains the brain. The ul- 

 factory lobes, which are directly connected with, and form 

 indeed a part of, the brain, enlarge at their ends, and 

 their broad extremities rest upon the upper side of the 

 cribriform plate, sending through it immense numbers of 



