Lateral Wall of the Cavum Nasi in Man. 669 



IV The i^NLAGEs of the Sinus Paranasales 



After the preceding consideration of the meatus nasi and the 

 conchae nasales, and the accessory folds and furrows, the genesis 

 of the sinus paranasales becomes much simplified and fairly easy 

 of interpretation. That all of the paranasal chambers develop 

 from preformed or preexisting furrows is certainly in accord with 

 my observations. Since the paranasal or accessory cavities 

 develop from preformed furrows and recesses, it is difficult to 

 say just when they begin to establish anlages. I, however, believe 

 that anlages are established much earlier than is generally sup- 

 posed — in fact the furrows and recesses from which the paranasal 

 sinuses develop are in a sense the 'primitive' anlages of these 

 chambers. The early tendency for the sinuses to establish their 

 'first' anlages may be no mean factor in making the recesses and 

 furrows what they early are. 



The preexisting spaces from which paranasal air chambers 

 may develop, according to my studies, are: (1) the suprabullar 

 recess, (2) the bullar furrow, (3) the infrabullar furrow, (4) the 

 infundibulum ethmoidale, of the descending ramus of the meatus 

 nasi medius; (5) the frontal furrows, (6) the frontal recess, of the 

 ascending ramus of the meatus nasi medius; (7) the ventral and 

 superior extremity of the meatus nasi superior; (8) the recessus 

 superior, (9) the recessus inferior, of the meatus nasi superior; 

 (10) the meatus nasi suprema I. 



Of the above named spaces we rarely find air cells developing 

 from the infrabullar furrow, and only occasionally from the bul- 

 lar furrow. I, however, find that rather frequently posterior 

 ethmoid cells develop from the inferior and superior recesses of the 

 meatus nasi superior, and about 75 per cent of specimens in 

 which the meatus suprema I persists we find a posterior ethmoidal 

 cell developing from the latter meatus (the meatus nasi suprema 

 I is present in about 62.5 per cent of adult specimens). I find 

 that the remainder of the aforementioned spaces are quite con- 

 stant in cell development. We must, however, remember that 

 the development of cells from the frontal furrows and recess is 

 very variable. 



