THE NASAL CAVITY 



1207 



caused by unusually thick walls of bone, bulging inward of the facial or nasal walls, and through 

 retention of teeth. Incomplete division into two parts through the presence of a septum has 

 several times been observed. Communication with ethmoidal cells and with the cavity of the 

 orbital process of the palate bone sometimes exists. 



Frontal sinus [sinus frontalis] (figs. 78, 964, 968). — The paired frontal sinuses, 

 separated from each other by a bony septum, have in general the shape of a three- 

 sided pyramid with the base below and the apex formed above in the frontal 

 squama. In the base near the septum is located the superior aperture of the 

 infundibulum which, it will be recalled, opens inferiorly at the anterior extremity 

 of the hiatus semilunaris. 



The form and size of the frontal sinuses are exceedingly variable. They may extend back- 

 ward in the orbital part of the frontal bone as far as the suture between it and the small wing of 

 the sphenoid; laterally into the zygomatic process; upward toward the coronal suture. The 

 capacity of the sinus, as determined in a small number of cases, varied from 3 to 7.8'ccni. 

 (Briihlj. Asymmetry of the septum is frequently observed. Absence of one of the sinuses is 

 not a rare condition; absence of both is occasionally encountered. 



Fig. 968. — Left Nasal Cavity. (Rauber-Kopsch. 



Opening of 

 sphe- 

 Hypophysis noidal sinus 



Spheno- 

 ethmoidal recess 



Choanal arch - 

 Pharyngeal tonsil -- 

 Torus tubarius" 

 Levator cushion 

 Anterior lip of 

 tubal aperture 



Salpingo- 

 pharyngeal 

 fold 



Naso-pharvngeal 

 : meatus Sound 



Uvula in naso- / 



lacrimal g'S 

 canal -S « 

 •3" 









Ethmoidal cells [cellulse ethmoidales] (figs. 965, 968). — The openings of the 

 anterior cells into the semilunar hiatus and infundibulum, and of the posterior 

 cells at the superior meatus have already been described. 



Communications between the ethmoidal cells and the sphenoidal and maxillary sinuses are 

 not rare; the cavity in the orbital process of the palate bone may open into the posterior cells. 

 In old age, foramina through the lamina papyracea may appear, leading to the introduction of 

 air into the orbit. 



Sphenoidal sinus [sinus sphenoidalis] (figs. 964, 965, 966).— The apertures of 

 the paired sphenoidal sinuses are, on account of the mucous membrane covering, 

 much smaller than they are in the dried skull. They lie in the anterior wall near 

 the septum, nearer the roof than the floor, and open into the spheno-ethmoidal 

 recess. 



Extension of the sphenoidal sinuses backward and also into neighbouring processes, and 

 communication with ethmoidal cells and with the small cavity of the orbital process of the palate 

 are not unusual. The capacity of the sinus varies between 1 and 4.2 ccm. (Briihlj. 



Functions of the paranasal sinuses. — Various functions have been attributed to the sinuses 

 near the nose, none of which is entirely satisfying. Mediaeval anatomists proposed that these 

 cavities contributed to the resonance of the voice, or that they supplied the mucus by which the 

 nasal cavity is kept moist. Lightening the skull, warming the inspired air and taking part, 

 indirectly, in the sense of smell ai-e functions assigned by anatomists of later times. 



The mucous membrane of the nose [membrana mucosa nasi]. — The nasal cav- 

 ity is completely lined with mucous membrane, which inferiorly, at the limen nasi 

 blends with the skin covering the walls of the vestibule (p. 1204). Posteriorly 

 it joins the mucous membrane of the pharynx and palate. It covers some of the 



