THE NASAL CAVITY. 



223 



front, at the inner side, where the frontal sinus intervenes. This sinus extends 

 downward, mesially, almost to the top of the lachrymal groove. The inner and 

 lower walls, separating the orbit from the nasal cavity and the antrum respectively, 

 are very thin and offer little resistance to a tumor or a foreign body. The great 

 wing of the sphenoid in the outer wall is thick, except just at the edge of the 

 sphenoidal fissure ; it separates the orbit from the middle cranial fossa. The outer 

 wall just behind the anterior border is thin, where it cuts off union with the 

 temporal fossa. 



The Nasal Cavity. — The nasal cavity of each side has an anterior and a pos- 

 terior opening, a roof, a floor, an outer wall, and an inner, the septum^ which, when 



Fig. 255. 



Crista galli 



Partition sepa- 

 rating frontal 

 sinus from orbit 



Sup. turbinate 



Lower part of 

 infundibulum 



Ethmoidal 

 bulla 



Nasal septum 



Antrum 



Frontal 



sinus 



Frontal bone, 

 roofing-in 

 ethmoidal 

 cells 



Middle tur- 

 binate 



Antrum 



Inferior 

 turbinate 



Floor of nasal fossae 



Inferior meatus 



Front section of skull through plane of outer border of orbits. Arrows pass through communication between 



antrum and middle meatus. 



the cartilage is present, completely separates it from its fellow. The anterior 

 common opening of the two cavities is shaped like an inverted ace of hearts, 

 bounded above by the border of the nasal bones and elsewhere by the superior 

 maxillae. In the middle of the floor of the opening is the anterior nasal spine, 

 resembling closely the bow of a boat. The anterior edge where the two bones meet 

 is the cutwater, and above is a triangular surface, the deck, bounded by a sharp 

 line, which runs outward, forming the lower border of the opening. In the adult 

 this line is usually continuous with the lateral border of the opening, but in infants' 

 skulls the line passes from the side onto the anterior surface of the maxillary bone. 

 Another line a little behind this, starting inside the nose at the front of the inferior 

 turbinate crest, runs close to the line from the spine. Though these lines are usually 



