THE SINUS SPHENOIDALIS 161 



during childhood has evidently been underestimated. 

 Many writers quote Toldt's statement, that in the develop- 

 ment of the sinus sphenoidalis the resorption process is 

 noticeable in the third year, reaches the sphenoid bone in 

 the sixth or seventh year, and in the eighth to the tenth year 

 really becomes a cavity in the sphenoid bone. The scarcity 

 of anatomic material showing the conditions present dur- 

 ing childhood is probably responsible for such conclusions. 

 Figs. 15, 16, 18, 22, 27, 29, and 31 show approximately the 

 average development as found in the given ages in this 

 series, and the extent of pneumatization is seen to be much 

 greater than in the cases observed by Toldt. 



The average diameters of the sinus sphenoidales as found 

 in the specimens of the various ages studied in this series 

 are given in the following table. The average distance from 

 the superior border of the ostia sphenoidalia to the level of 

 the cribriform plate of the ethmoid, the average diameters 

 of the ostia, and the thickness of the sphenoidal septum are 

 also given. All measurements are in millimeters. 



The marked tendency of the sinus sphenoidalis to develop 

 posterolaterally more rapidly than it does directly pos- 

 teriorly (Fig. 22) is such that in the average case the lateral 

 wall of the sinus becomes quite thin (one millimeter or less 

 in the thinest portion) by the end of the second or during 

 the third year, while the septum sphenoidale still remains 

 relatively thick first reaching an average of one millimeter 

 or less in the ninth year. (See table p. 162.) Thus this 

 early posterolateral resorption of the osseous wall soon brings 

 the sinus into close relation to those cranial nerves which 

 pass just lateral to the body of the sphenoid (Figs. 21, 30, 



32, 39, 45, 47, 50, and 55), and shows an anatomic basis for 

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