THE ENTIRE SKULL 489 



NASAL FOSSAE. 



The anterior part of the conjoined frontals is united with the bones 

 of the face to form a thin-walled nasal chamber, almost completely 

 filled by the ethmoid, the maxillo-turbinal, and the vomer. Indeed, 

 the investing bones are in great measure moulded on the outer surface 

 of the lateral ethmoids, and a cast of the nasal chamber has the form 

 and nearly the size of the ethmoid, vomer, and turbinal when removed 

 from the skull (Fig. 392). If the nasal chamber be bisected longitu- 

 dinally, and the mesethmoid, the median plate of the frontal, the lateral 

 ethmoid, and the maxillo-turbinal be carefully broken away, its invest- 

 ing walls become visible (Fig. 398). The nasal chamber is narrower 

 above than below, and narrower in front and behind than in the middle. 

 Its greatest height, which is behind, is but a fifth less than its greatest 

 median antero-posterior length below. Its greatest width is on the 

 floor, on a transverse line joining the lower edges of the lachrymal 

 bones, and is about a third less than its length. It is divided by a 

 median vertical partition, composed of the frontal, the nasal, the mes- 

 ethmoid, the vomer, and plates of cartilage, into equal halves known 

 as the nasal fossae or nasal sinuses. Each nasal fossa, therefore, con- 

 tains a lateral ethmoid and a maxillo-turbinal. It presents inner, 

 outer, and posterior walls, a floor, a roof, and anterior and posterior 

 openings. 



The inner or median wall of each nasal fossa (Fig. 391) is vertical 

 and flat, but may be bowed inward or outward. It is high behind 

 and low in front, and is formed above by the median plates of the 

 frontal and the nasal, for the larger part of its extent by the meseth- 

 moid with its forward continuation, the septal cartilage, and at the 

 lowest part by the vomer. The lower edge of the partition is higher 

 behind, where it is free, than in front, where it is attached to the 

 middle line of the floor of the general nasal chamber. The space 

 under its posterior part between the vomer and the palatines permits, 

 even in the natural state, one nasal fossa to communicate with the 

 other. 



The posterior wall of the nasal fossa is convex from above down- 

 ward, and is almost exclusively formed by the anterior surface of the 

 cribriform plate of the ethmoid. It gives attachment to the posterior 

 ends of the scrolls of the lateral ethmoid. Above the cribriform plate 

 the frontal forms a small upper part of the posterior wall, which is 



