80 THE NASAL ACCESSORY SINUSES IN MAN 



diameters of the sinus during these early periods. In the 

 case of a child eight days old the sinus diameters were found 

 to be 8.2 mm. anteroposteriorly, 3.3 mm. vertically, and 2.8 

 mm. laterally (Fig. 17 was drawn from this specimen). 

 As the body of the maxilla increases in size there is a cor- 

 responding increase in the extent of pneumatization. Up 

 until the eighth year the diameters of the sinus maxillaris 

 increase at a rate which was found to average approximately 

 2 mm. each year in both the vertical and the lateral di- 

 ameters, and 3 mm. anteroposteriorly. After the eighth 

 year the development of the sinus advances more slowly in 

 all directions, reaching in the fifteenth to the eighteenth 

 year a form which approximates the adult type, later changes 

 being shown chiefly in the postero-inferior angle, which de- 

 scends as the third molar tooth erupts. 



The following table shows the average diameters of the 

 ostia maxillaria and of the sinus maxillares, as found in the 

 various ages. All measurements are given in millimeters. 

 (In considering the relation of the sinus floor to the nasal 

 floor, measurements preceded by a plus sign indicate that 

 the average sinus floor was found to be the given distance 

 above the level of the nasal floor. Measurements preceded 

 by a minus sign indicate that the average sinus floor was the 

 given distance below the level of the nasal floor.) 



From this table it is seen that the floor of the sinus 

 maxillaris, in an average case, reaches a level equal to that 

 of the floor of the nasal fossa during the eighth year, and 

 in the majority of older cases is from 1 mm. to 5.5 mm. below 

 the level of the nasal floor, regardless of the sex of the indi- 

 vidual. Reschreiter regarded a floor of the sinus maxillaris 

 below the level of the nasal floor as a male characteristic. 



