EMBRYOLOGIC CONSIDERATIONS 43 



mucosa attached, four ethmoidal conchae were present in 

 2 per cent, of the cases, three in 92 per cent., and two in 

 only 6 per cent., yet two is the number most frequently 

 described in anatomic works. 



All ethmoidal cells, the frontal and maxillary sinuses, 

 have their origin from preformed grooves or furrows between 

 the folds which develop on the lateral nasal wall. The 

 meatus nasi medius soon becomes the most complex portion 

 of the nasal cavity, and developing from it and extending 

 into the surrounding areas are extensive processes of pneu- 

 matization which are termed the cellulaB ethmoidales anterior, 

 the sinus maxillaris, and the sinus frontalis. 



