26 SMELL, TASTE, ALLIED SENSES 



naturally into four sets, the maxillary, frontal, and sphe- 

 noidal sinuses and the ethmoidal cells. Each maxillary 

 sinus is a large space in the maxillary bone above the 

 teeth. It opens by a considerable sli t into the anterior part 

 of the middle meatus. (Figs. 1 and 2). The frontal sinus,in 

 the frontal bone also opens into the middle meatus at a 

 point above and anterior to the opening of the maxillary 

 sinus. Each sphenoidal sinus opens into the posterior end 

 of the appropriate olfactory cleft in a region known as the 

 spheno-ethmoidal recess. The remaining accessory nasal 

 spaces, the ethmoid cells, are more or less variable ; some 

 of them open into the middle meatus by several apertures 

 well above the slit for the maxillary sinus. Others open, 

 more commonly by a single aperture, into the superior 

 meatus. In addition to these various openings, the naso- 

 lacrimal duct, by which the lacrimal secretions from the 

 eye are carried to the nasal cavity, opens between a 

 pair of lips on the lateral wall of the inferior meatus near 

 its anterior extremity, 



2. Nasal Membranes. The nasal vestibule is lined 

 with a delicate continuation of the outer skin. The walls 

 of the deeper part of the nasal cavity are covered with a 

 mucous membrane which is divisible into two regions, the 

 restricted olfactory region in the dorsal part of the cavity 

 and the much more extended respiratory region embrac- 

 ing the remainder of the cavity. 



The mucous membrane of the respiratory region is 

 reddish in color and consists of a pseudo-stratified epi- 

 thelium containing ciliated cells and basal cells backed up 

 by a well developed tunica propria. (Fig. 3.) The cilia 

 of this region lash towards the choana. The secretion 

 covering the surface of the epithelium comes from numer- 



