994 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



The Nasal Cavity (Cavum Nasi; Nasal Fossa). 



The nasal chambers are situated one on either side of the median plane. They 

 open in front through the nares, and communicate behind through the choanae 

 with the nasal part of the pharynx. The nares are somewhat pear-shaped apertures, 

 each measuring about 2.5 cm. antero-posteriorly and 1.25 cm. transversely at its 

 widest part. The choanae are two oval openings each measuring 2.5 cm. in the 

 vertical, and 1.25 cm. in the transverse direction in a well-developed adult skull. 



For the description of the bony boundaries of the nasal cavities, see pages 194 

 and 195. 



Inside the aperture of the nostril is a slight dilatation, the vestibule, bounded 

 laterally by the ala and lateral eras of the greater alar cartilage, and medially by 

 the medial crus of the same cartilage. It is lined by skin containing hairs and 

 sebaceous glands, and extends as a small recess toward the apex of the nose. Each 

 nasal cavity, above and behind the vestibule, is divided into two parts : an olfactory 

 region, consisting of the superior nasal concha and the opposed part of the septum, 

 and a respiratory region, which comprises the rest of the cavity. 





Spheno-ethmoidal recess 



Pharyngeal orifice of auditor y tube Phanjngeal recess 



Fio. 855.- Lateral wall of nasal cavity. 



Lateral Wall (Figs. 855, 856). On the lateral wall are the superior, middle, and 

 inferior nasal conchae, and below and lateral to each concha is the correspond- 

 ing nasal passage or meatus. Above the superior concha is a narrow recess, 

 the sphenoethmoidal recess, into which the sphenoidal sinus opens. The superior 

 meatus is a short oblique passage extending about half-way along the upper border 

 of the middle concha; the posterior ethmoidal cells open into the front part of this 

 meatus. The middle meatus is below and lateral to the middle concha, and is 

 continued anteriorly into a shallow depression, situated above the vestibule and 

 named the atrium of the middle meatus. On raising or removing the middle concha 



