136 THE NASAL ACCESSORY SINUSES IN MAN 



All measurements are given in millimeters. The level of the 

 ostia and the superior level of the sinuses were in all cases 

 measured from the level of the nasion. Thus measurements 

 preceded by a minus sign indicate that the average level was 

 the given distance inferior to the nasion, while those preceded 

 by a plus sign indicate the given distance superior to the 

 nasion. 



The resorption of the diploe in the vertical portion of the 

 frontal bone is seldom such as to make the sinuses of the two 

 sides quite symmetric. The general outline of the sinuses 

 often suggests an attempt at symmetry, although one or 

 more of the diameters may show considerable variation. 

 Not uncommonly, however, the two sinuses are of an entirely 

 different form. Irregularity in the rate of resorption on the 

 two sides often produces a deviation of the septum frontale. 

 The position of the septum frontale is, in the great majority 

 of cases, median at its inferior portion, but in a few instances 

 this portion showed variations of from 2 to 6 mm. from the 

 median line. The superior portion of the septum, however, 

 usually shows a slight deviation to one side or the other, 

 the deviation being away from the more rapidly developing 

 sinus. Occasionally a case is found in which one of the 

 sinuses is poorly developed and the sinus from the other side 

 has developed so far past the median line that the resulting 

 deviation of the septum is such that it forms a part of the 

 anterior wall of the deficiently developed sinus. However, 

 in cases where the interfrontal suture persisted (metopic 

 skulls) , no instance was found in which a sinus had extended 

 past the median line, regardless of the extent of pneumatiza- 

 tion on the opposite side. 



In 101 cases (202 frontal sinus areas) having the mucosa 



