668 



THE NOSE. 



into those cavities ; but the siDheno-palatine foramen is covered over by the 

 Schneiderian membrane, so that no such opeuing exists in the recent nasaj 

 fossa. 



In the middle meatus, the apertm-e of the infundibulum is nearly hidden by 

 an overhangfing' fold of membrane ; it leads directly into the anterior ethmoidal 

 cells, and through them into the frontal sinus. Below and behind this, the 

 passage into the antrum of Highmore is surrounded by a circular fold of the 

 pituitary membrane (sometimes prominent and even slightly valvular), which 

 leaves a circular aperture much smaller than the foramen in the bony meatus. 



In the loiver mcutm the inferior orifice of the nasal duct is defended by one or 

 two folds of membrane ; and when there are two, the folds are often adapted so 

 accurately together as to prevent even air from passing back from the cavity of 

 the nose to the lachrjnnal sac. 



In the roof the apertures in the cribriform plate of the ethmoid bone are closed 

 by the membrane, but the openings into the sphenoidal sinuses receive a pro- 

 longation from it. 



In the foor the incisor foramen is in the recent state generally closed. Some- 

 times, however, a narrow funnel-shaped tube of the mucous membrane descends 

 for a short distance into the canal, but is closed before it reaches the roof of the 

 palate. Vesalius. Stenson. and Santorini, believed that this tube of membrane 

 opened generally into the roof of the mouth by a small aperture close behind the 

 interval between the central incisor teeth. Haller, Scarjia, and more recently, 

 Jacobson. find that in man it is usually closed, and often difficult of detection. 

 (See Cuviers Report on a paper by Jacobson, "Annales du Museum d"Hist. 

 Naturelle ; " Paris, 1811 ; vol. xviii. p. 412.) 



MUCOUS MEMBRANE. 



The pituitary or Schneiderian membrane, which lines the cavities of 

 the nose, is a highly vascular mucous membrane, inseparably united, 



Fix. 483. 



Fig. 4S3. — Outer Wall of the Left Nasal Fossa, covered by the PiTriTAF.r 



Membrane (Arnold), f 

 1, frontal Lone ; 2, left nasal boue ; 3, superior maxillary ; 4, body of the sphenoid 

 with the sphenoidal sinus ; 5, in-ojcction of the membrane covering the upjier spongy 

 bone ; 6, that of the middle ; 7, that of the lower ; the upper, middle, and lower 

 meatuses are seen below the corresponding sjaongy bones ; 8, opening of the Eustachian 

 tube ; 9, depression of the lining membrane of the nose in the anterior x^alatine canal. 



