114 THE NASAL ACCESSORY SINUSES IN MAN 



accessory ostia, while in all other specimens accessory ostia 

 were present in only 7.7 per cent, of cases. 



Zuckerkandl regarded pressure from septal spurs or from 

 enlarged middle conchse as occasional factors in the produc- 

 tion of ostia accessoria. In this series no case with an 

 accessory ostium showed these conditions to be present in a 

 sufficient degree to exert any apparent influence on the de- 

 velopment of an accessory opening. 



The superior wall, or roof, of the sinus maxillaris is a thin 

 plate of bone (its superior surface being the facies orbitalis 

 maxillae), the central and posterior portions of which vary 

 from 0.5 to 1.5 mm. in thickness. Along two ridges which 

 project into the sinus and near the anterior margin, the 

 bone is usually of a greater thickness. The more constant 

 of the two ridges is the one which forms the inferior wall of 

 the above-mentioned canalis infraorbitalis (Figs. 25, 26, 

 42, and 52). The second ridge is well marked in the major- 

 ity of cases, and extends laterally along the roof from the 

 posterior margin of the ostium maxillare (Figs. 33, 39, 45, 

 and 54). Its prominence decreases as it passes laterally, 

 and usually disappears just medial to the canalis infra- 

 orbitalis. 



Not uncommonly the cellulse ethmoidales, in their infero- 

 lateral development, extend for a short distance (2 to 4 mm.) 

 into the roof of the sinus ; and in rare instances the develop- 

 ment may be such that an aberrant posterior ethmoidal 

 cell occupies the area which would ordinarily be the postero- 

 superior angle of the sinus maxillaris (Fig. 50). 



The posterior wall of the sinus maxillaris is the most 

 regular of all its boundaries. In an average case it varies 

 from 0.5 to 3 mm. in thickness, the portions near the angles 



