NASAL CAVITIES AND SINUSES. 



63 



The roof is horizontal in its middle part, but sloped downwards before and 

 behind. The middle part is formed by the cribriform plate of the ethmoid 

 bone, the fore part by the frontal and nasal bones, and the back part by the 

 sphenoidal spongy bone. 



The floor, formed of the palate plates of the maxillary and palate bones, 

 is smooth, and concave from side to side. Towards its anterior extremity is 

 the superior orifice of the incisor canal. 



Fig. 54. VERTICAL ANTERO- Fij. 54. 



POSTERIOR SECTION OP A 

 PART OF THE CRANIUM, TO 

 THE LEFT OF THE MIDDLE, 

 VIEWED FROM THE INNER 

 SIDE, TO SHOW THE OUTER 

 WALL OF THE LEFT NASAL 

 FOSSA, &o. i 



1, nasal bone ; 2, nasal pro- 

 cess of the superior maxillary 

 bone ; 3, ascending plate of the 

 palate bone ; 4, superior turbi- 

 nated bone of the ethmoid 

 below it the superior meatus, 

 behind it the opening into the 

 left sphenoidal sinus ; 5, the 

 middle turbinated bone below 

 it the middle meatus, in which 

 are seen the uncinate process of 

 the ethmoid, and, between it 

 and the inferior turbinated 

 bone, the opening into the 

 maxillary sinus ; superiorly 

 and anteriorly, the opening of the infundibulum and anterior ethmoidal cells ; behind it, 

 and above 3, the spheno-palatine foramen ; 6, the inferior turbinated bone below it the 

 inferior meatus x x , below these marks the section of the palatine plates of the left 

 palate and superior maxillary bones ; 7, the left frontal sinus ; 8, the left sphenoidal 

 sinus ; 9, the left optic foramen in the root of the lesser wing of the sphenoid and 

 anterior clinoid process; 10, the ridge of the dorsum sellse divided ; and between 9 and 

 10, the sella turcica; 11, is placed on the posterior surface of the petrous bone, close to 

 the internal auditory meatus ; 12, is placed on the basilar process of the occipital bone, 

 close to the foramen lacerum posterius ; 13, is placed below the anterior condyloid 

 foramen ; 14, left styloid process ; 15, external, and 16, internal pterygoid processes ; 

 17, posterior palatine canal and grooves. 





The external wall is the most extensive. The bones which take part in 

 its formation are the nasal, superior maxillary, ethmoid, inferior spongy, 

 and palate bones, aud the internal pterygoid plates. The superior and 

 inferior turbinated processes of the ethmoid bone (superior and middle 

 turbinated bones), and the inferior spongy bone, projecting inwards, 

 overhang three galleries or meatus. The superior meatus, very short, is 

 placed between the superior and inferior turbinated processes of the ethmoid 

 bone ; into it open anteriorly the posterior ethmoidal cells, and posteriorly 

 the spheno-palatine foramen and sphenoidal sinus. The middle meatus, the 

 space between the inferior turbinated process of the ethmoid and the inferior 

 spongy bone, communicates at its fore part with the anterior ethraoidal cells, 

 and, by means of the infundibulum, with the frontal sinus, while in its 

 middle is the opening of the maxillary sinus. The inferior meatus, longer 

 than the others, lies below the inferior spongy bone, between it and the floor 

 of the nasal cavity ; in its fore part is the orifice of the nasal duct. 



