SPONGY BONES AND MEATUSES. 



135 



meatuses, and occupies the posterior half of the space included by the ver- 

 tical lines before mentioned. Into it the posterior ethmoidal sinuses open 

 at the front ; and at its posterior part, in the dried bone, is the spheno- 

 palatine foramen by which the nerves and vessels enter the nose. 



The middle meat us (fig. 31, 7 ) is longer than the preceding; it is 

 curved upwards in front, and reaches all across the space referred to on 

 the outer wall. Anteriorly it communicates by a funnel-shaped passage 

 (infundibulum) with the frontal sinus and the anterior ethmoidal cells ; 

 and near its middle is a small aperture, which leads into the cavity of the 

 upper jaw. 



The inferior meatus (fig. 31, 8 ) is straighter than the middle one, and 

 rather exceeds the width of the included space on the outer wall ; and 



Fig. 31. 



1. Upper spongy bone. 



2. Middle spongy bone. 



3. Inferior spongy boae. 



4. Square part of the ethmoid bone. 



6. Upper ineatus. 



7. Middle meatus. 



8. Lower meatus. 



9. Rudimentary fourth meatus. 

 10. Vestibule of the nasal cavity. 



The woodcut shows also the aper- 

 tures of the glands of the nose. 



SPONGY BONES AND MEATUSES or THE NASAL CAVITY. 



when the bone is clothed by the mucous membrane it extends still further 

 forwards. In its front is the opening of the ductus ad nasum. 



Occasionally there is a small fourth or rudimentary meatus above the 

 rest (tig. 31, 9 ), which communicates with a posterior ethmoidal cell. 



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

 tinct anterior opening in 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 the parts bounding them, have been before described (pp. 

 42 and 126). 



The mucous membrane lining the nasal fo?sa is called the pituitary or 

 Schneiderian membrane ; and from its blending with the periosteum it 

 acquires much strength. It is continuous with the integument at the nos- 

 tril, and with the membrane lining the pharynx through the posterior 

 opening : moreover, it is also continuous with the mucous membrane of 

 the eyeball, and with that of the different sinuses, viz., frontal, ethmoidal, 

 sphenoidal, and maxillary. 



The foramina in the dry bones, which transmit nerves and vessels, are 

 entirely closed by the membrane, viz., the incisor, spheno-palatine, the 

 holes in the cribriform plate, and the foramen for the nasal nerve and 



