REGIONS OF THE NOSE. 671 



ethmoiclal cells ; and in some cases there is a second opening into 

 the antrum close above the lower turbinate bone. 



The inferior meatus (fig. 235), is wider than the middle one, and Lower 

 extends the whole length of the hard palate. Near its anterior meatus - 

 extremity is the opening of the nasal duct (fig. 237). 



Above the superior meatus, in an angle formed by the roof, there Spheno- 

 is a vertical depression called the spheno-ethnwidal recess (fig. 237), on 

 the posterior wall of which the sphenoidal sinus opens ; and occasion- 

 ally a small fourth meatus, communicating with a posterior ethmoidal A fourth 

 cell, is present between the recess and the superior meatus. somethnes 



In front of the attached border of the middle turbinate bone there 

 is usually to be seen a faint ridge, the agger nasi (fig. 237), directed Agger nasi, 

 obliquely downwards and forwards, and forming the upper boundary 

 of a slight hollow known as the atrium of the middle meatus (fig. and atrium. 

 237). 



The nares. In the recent condition of the nose each fossa has a N 

 distinct anterior opening on the face, and another in the pharynx ; 

 but in the skeleton there is only one common opening in front for 

 both sides. These apertures and their boundaries have been before 

 described in the anatomy of the face. 



The MUCOUS LINING OF THE NASAL FOSSAE is called the pituitary MUCOUS 

 or Schneiderian membrane, and is blended with the subjacent perios- 

 teum or perichondrium. It is continuous with the skin at the 

 nostril, with the membrane lining the pharynx through the posterior 

 nares, and with the conjunctiva through the nasal duct ; and it sends 

 prolongations to line the different sinuses, viz., frontal, ethmoidal, 

 sphenoidal, and maxillary. 



The apertures in the dry bone which transmit nerves and vessels, some fora- 

 viz., the incisor and spheno-palatine foramina, the holes in the mma closed > 

 cribriform plate, and the foramen for the nasal nerve and vessels, 

 are entirely closed by the membrane ; and the openings leading to others 

 the sinuses are reduced in size by the prolongations passing through by^t" 18 

 them. At the termination of the nasal duct the mucous membrane 

 forms a single or double fold, which is sometimes sufficient to close 

 the opening and prevent air entering the canal from the nose. 



Over the middle and lower turbinate bones (to a greater extent Folds on 

 on the latter) the mucous membrane is thickened and projected 

 beyond the edges of the bones by the large submucous vessels, so 

 that the meatuses are deeper and longer in the recent state than in 

 the dried skull. 



The appearance and structure of the lining membrane differ in the Three 

 upper and lower parts of the nasal fossa, and near the anterior open- 

 ing, whence a division of the cavity is made into three portions, 

 which are termed respectively the olfactory region, the respiratory 

 region, and the vestibule. 



The vestibule (fig. 237) is the slightly dilated portion of the Vestibule, 

 cavity immediately within the nostril. It is bounded by the 

 cartilage of the aperture and the ala of the nose ; and its wall is 

 more flexible than that of the part above. The lining membrane of 



