774 THE NOSE. 



dimension of parts, which depend on the arrangement of the lining mem- 

 brane, viz. 



Throughout the whole of the nasal fossae it is to be observed that 



First, owing to the thickness of the membrane in question, (which not only lines 

 the walls of the fossae, but covers the spongy bones on both sides,) the nasal cavity is 

 much narrower in the recent state. Second, in consequence of the prolongations of 

 membrane on their free margins, the turbinate bones, and more particularly the 

 lower pair, appear in the recent state to be both more prominent, and longer in the 

 direction from before backwards, than in the dried skull. Third, by the arrange- 

 ment of the mucous membrane round and over the orifices which open into the 

 nasal fossae, some of the foramina in the bones are narrowed, and others completely 

 closed. 



In the individual parts of the nasal fossae the following particulars are to be 

 noticed. 



In the upper meatus, the small orifice which leads into the posterior ethmoidal 

 cells is lined by a prolongation of the thin mucous membrane which continues into 

 those cavities ; but the spheno-palatine foramen is covered over by the Schneiderian 

 membrane, so that no such opening exists in the recent nasal fossa. 



In the middle meatus the aperture of the infundibulum is nearly hidden by an 

 overhanging 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 lower meatus, 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 lachrymal 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 prolonga- 

 tion from it. 



In the Jloor 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, Scarpa, and, more recently, Jacob- 

 son, find that in man it is usually closed, and often difficult of detection. (See 

 Cuvier's 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, like that 

 investing the cavity of the tympanum, with the periosteum and peri- 

 chondrium over which it lies. It is continuous with the skin through 

 the nostrils ; with the mucous membrane of the pharynx through the pos- 

 terior apertures of the nasal fossae ; with the conjunctiva through the nasal 

 duct and lachrymal canaliculi ; and with the lining membrane of the several 

 sinuses which communicate with the nasal fossae. The pituitary membrane, 

 however, varies much in thickness, vascularity, and general appearance in 

 these different parts. It is thickest and most vascular over the turbiuato 

 bones (particularly the inferior), from the most dependent parts of which it 

 forms projections in front and behind, thereby increasing the surface to some 

 extent. On the septum nasi the pituitary membrane is still very thick and 

 spongy ; but in the intervals between the turbinate bones, and over the 

 floor of the nasal fossae, it is considerably thinner. In the maxillary, frontal, 



