NASAL CAVITIES 399 



The inferior meatus is the horizontal passage which lies 

 between ^the inferior concha and the floor and lateral wall 

 of the nasal cavity. It is placed posterior to the vestibule, 

 and the free border of the inferior concha turns downwards 

 and limits it anteriorly (Fig. 156). On this account, and 

 because its floor slopes downwards and posteriorly, the in- 

 ferior meatus is more accessible to the current of expired 

 air than to the current of inspired air. In the anterior part 

 of this meatus will be found the opening of the naso-lacrimal 

 duct which conveys the tears to the nasal cavity (Fig. 156). 



To bring the aperture of the naso-lacrimal canal into view, remove 

 a small portion of the anterior part of the inferior concha with the 

 scissors. 



The orifice of the naso-lacrimal duct varies in form, 

 according to the manner in which the mucous membrane is 

 arranged around it. Sometimes it is wide, patent, and circular ; 

 at other times the mucous membrane is prolonged over 

 the opening, reducing its size and acting as a flap valve to 

 the orifice. In some cases, indeed, the orifice may be so 

 minute that it is difficult to find. Its continuity with 

 the lacrimal sac should in all cases be established by passing 

 a probe from above downwards through the naso-lacrimal 

 canal (Fig. 64). 



A fourth meatus is generally present on the lateral wall of 

 the nasal cavity. This is due to the partial subdivision of 

 the superior concha into an upper and lower part by a short 

 groove which proceeds anteriorly from the anterior aspect 

 of the body of the sphenoid. This additional meatus is 

 termed the rccessus spheno-ethmoidalis, and in its posterior 

 part is the aperture of the sphenoidal air sinus (Fig. 156). 

 This orifice may be circular or slit-like, according to the 

 manner in which the~ mucous membrane is disposed around 

 it. 1 The upper portion of the superior concha which 

 is placed above this additional meatus is called the concha 

 suprema (Fig. 155, 10). 



To the narrow cleft-like portion of the nasal cavity which 

 extends from the roof to the floor between the septum 

 medially and the conchae laterally the term meatus communis 

 is applied; and the part of the cavity which lies posterior 



1 When the recessus spheno-ethmoidalis is absent, the sphenoidal air sinus 

 opens into the interval between the roof of the nasal cavity and the superior 

 concha. 



