478 CLARK. 



whichever anterior ethmoidal evagination develops first. This would 

 also explain how a great proportion of the frontal sinuses are not in con- 

 nection through the nasofrontal duct with the infundibulum ethmoidale. 

 Ernst Witt claims that the sinus frontalis and the cellulaj ethmoidales 

 arise from Arilage which developmental!}' are related very closely and 

 which may replace one another. 



It is difficult to account embryologically for an accessory nasofrontal 

 duct in this position. A possible explanation might be afforded if we 

 assume that coincident with the development of the evaginations from the 

 infundibulum, there developed from the upper anterior wall of the fossa 

 nasalis a long, slender evagination — a bulla nasalis anterioris — which 

 came to lie in the position described for the ductus nasofrontal acces- 

 sorius, and which later established a communication with the sinus 

 frontalis by fusion ; or, on the other hand, if we assume, instead of a bulla 

 nasalis anterioris, that from the sinus frontalis itself, the long evagination 

 developed and later established communication with the fossa nasalis. 

 In addition, it is possible that the sinus frontalis represents the dilated 

 upper extremity of the bulla nasalis anterioris, and that communication 

 with the vestibule of the frontal cells was attained by fusion as above. 



In conclusion I desire to thank Prof. J. Gordon Wilson for the 

 kind assistance he has given me in the identification of the structures 

 described. 



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