130 THE NASAL ACCESSORY SINUSES IN MAN 



considered as one which overlies the roots of all the molars 

 and the posterior portion of the second premolar. In many 

 cases only the molars come into close relation, and in a few 

 cases only the second and third molars are beneath the floor. 

 It is a very extensive floor, which advances so far anteriorly 

 as to overlie the first premolar, and in this series no case was 

 found in which the root of the canine was in relation to the 

 floor. In a few of the larger sinuses, however, the root of 

 the canine extended well up into the anterior wall of the 

 sinus. 



Regardless of the extent of the irregularities in the floor 

 of the sinus produced by resorption of the cancellous bone 

 surrounding the roots of the teeth, in no instance was the 

 mucosa lining the sinus found in direct contact with the root 

 of a healthy tooth. In all normal cases a thin layer of com- 

 pact bone was present between the roots of the tooth and 

 the mucosa; but in a few instances, where there had been 

 abscess formation at the root of a tooth, this intervening 

 plate of bone had been destroyed, thus allowing the root to 

 project into the sinus cavity, in direct contact with the over- 

 lying mucosa. 



Besides the recesses produced by the ridges on the alveolar 

 surface, pockets may be formed by osseous projections on the 

 anterior, or less frequently on the posterior, wall, or by folds 

 of mucosa independent of any irregularity in the underlying 

 bone, as found in the posteromedial angle of the sinus shown 

 in Fig. 47. Osseous ridges may, in rare instances, extend 

 sufficiently far toward the central portion of the sinus as to 

 form incomplete septa, or septulae (Fig. 35). Such forma- 

 tions have no embryologic significance, and are entirely 

 due to irregularity in the process of resorption. Ridges and 



