138 



SPECIAL ANATOMY OF THE SKELETON 



The Nasal Cavity. The nasal cavities (cavum nasi),or nasal fossae (Figs. 81 and 

 103), are two large, irregular cavities situated on either side of the middle line of 

 the face, extending from the base of the cranium to the roof of the mouth, and 

 separated from each other by a thin vertical septum, the septum of the nose 

 (septum nasi ossewn), formed by the perpendicular plate of the ethmoid and by 

 the vomer. Each cavity communicates by a large aperture, the anterior nasal 

 aperture (apertura pyriformis), 1 with the front of the face, and by the two posterior 

 nares (choance) with the nasopharynx behind. These fossae are much narrower 

 above than below, and in the middle than at the anterior or posterior openings; their 

 depth, which is considerable, is much greater in the middle than at either extremity. 

 The nasal fossae are surrounded by four other fossae above is the cranial fossa; 



PROBE FROM FRONTAL 



SINUS IN THE 



INFUNDIBULUM 



PROBE IN NASO- 

 LACRIMAL CANAL 



VERTICAL PLATE OF 

 PALATE BONE 



FIG. 103. Nasal cavity, right lateral wall, from the left. (Spalteholz.) 



laterally, the orbital fossae; and below, the cavity of the mouth. Each nasal fossa 

 communicates with four sinuses the frontal above, the sphenoidal behind, and 

 the maxillary and ethmoidal on the outer wall. Each fossa also communicates 

 with four cavities with the orbit by the lacrimal groove, with the mouth by the 

 anterior palatine canal, with the cranium by the olfactory foramina, and with the 

 sphenomaxillary fossa by the spheno palatine foramen; and they occasionally 

 communicate with each other by an aperture in the septum. The bones entering 

 into their formation are fourteen in number three of the cranium, the frontal- 

 sphenoid, and ethmoid, and all the bones of the face, excepting the malar and man, 

 dible. Each cavity is bounded by a roof, a floor, an inner and an outer wall. 



The upper wall, or roof (Fig. 104), is long, narrow, and horizontal in its centre, 

 but slopes downward at its anterior and posterior extremities; it is formed in front 

 by the nasal bones and nasal spine of the frontal, which are directed downward 

 and forward; in the middle, by the cribriform plate of the ethmoid, which is hori- 



1 In the skull freed of soft parts the anterior nasal cavities open in front by the apertura pyriformis. 

 skull with the soft parts in place they open by the anterior nares. 



In the 



