THE SENSE OF SMELL. 



849 



According to Lee l and others, the equilibrium of rest and motion, or static 

 and dynamic equilibrium, depends upon the irritation of different nerve-ter- 

 minals. The manner of action of the latter has been considered. As to the 

 nervous mechanism on which static equilibrium depends, Lee is of the opinion 

 that the knowledge of the position of the head while at rest comes from the rela- 

 tion of the otoliths in the vestibular sacs to the nerve-endings on the maculce 

 acusticce. These otoliths form considerable masses in the ears of fishes, and the 

 intensity and direction of their pressure upon hair-cells must vary with the 

 spatial relations of the head, and thus be comparable, in the sense of posi- 

 tion which they arouse, to the tactile sensations derived from the soles of 

 the feet in man. 



P. SMELL. 



The complex paired cavity of the nose is divisible into a lower respiratory 

 and an upper olfactory tract, the mucous membrane over each of which is 

 distinctive. The covering of the respiratory tract is known as the Schneider- 

 ian or pituitary membrane; its surface is overlaid with cylindrical ciliated 

 epithelium, the ciliary current of which is directed posteriorly toward the 

 pharynx. 



The Schneiderian membrane lines the lower two-thirds of the septum, the 

 middle and inferior turbinated bodies, and the bony sinuses which communi- 

 cate with the nasal chamber. The mem- 

 brane upon the turbinated bodies and 

 the lower part of the septum is composed 

 largely of erectile tissue. 



The function of the respiratory tract 

 is threefold : it restrains the passage 

 of solid particles into the lungs; it 

 warms the air inspired to approximately 



FIG. 290. Section of olfactory mucous mem- 

 brane (after V. Brunn) : the olfactory cells are in 

 black. 



FIG. 291. Cells of the olfactory region (after V. 

 Brunn) : a, olfactory cells ; b, epithelial cells ; n, 

 central process prolonged as an olfactory nerve- 

 fibril ; I, nucleus ; c, knob-like clear termination 

 of peripheral process ; h, bunch of olfactory hairs. 



the temperature of the body ; and it gives up moisture sufficient nearly to 

 saturate the air. 



1 Journal of Physiology, xv. p. 31 1 ; xvii. p. 192. 

 54 



