THE BUCCAL CAVITY. 75 



Anteriorly it presents the opening of the frontal and eth- 

 moidal sinuses, and about its centre is the opening of the 

 antrum of Highmore. The superior meatus, situated at 

 the posterior third of the nasal cavity, communicates 

 with the posterior ethmoidal cells and the sphenoidal 

 sinus. The floor of the nose is formed by the superior 

 surface of the horizontal processes of the superior maxil- 

 lary and palate bones. It is smooth, slightly concave 

 from side to side, and broader at the centre than at 

 either extremity. The roof consists of three portions, 

 anterior, middle, and posterior. The anterior portion 

 slopes downward and forward, and is formed by the 

 nasal bones and the spine of the frontal ; the middle 

 portion is horizontal, and is formed by the cribriform 

 plate of the ethmoid ; the posterior is the anterior and 

 under surface of the body of the sphenoid, which slants 

 backward and downward. The anterior opening, with 

 the triangular cartilage in place, is semi-cordiform ; the 

 posterior opening is elliptical. 



The cavity of the mouth is below the nasal cavities 

 and extends in the skull, from the inner surface of the 

 alveolar processes of the superior and inferior maxillary 

 bones and the inner surfaces of the teeth, backward to 

 the posterior border of the hard palate. It presents for 

 examination a roof (the hard palate) and anterior and 

 lateral boundaries. The roof is formed by the horizontal 

 processes of the superior maxillary and palate. It is 

 rough, concave from side to side and from front to back, 

 and presents in the median line a ridge, which is more 

 or less well marked. Behind the central incisor teeth is 

 the anterior palatine canal; on each side posteriorly, 

 and just internal to the last molar tooth, is the opening 

 of the posterior palatine canal, and running forward 

 from this is a well-marked groove for the artery and 



