Lateral Wall of the Cavum Nasi in Man. 681 



Its further development depends of course, just as in the other 

 sinuses, upon the simultaneous growth of the sac and the resorp- 

 tion of bone. In this manner the sphenoidal cavity becomes well 

 established in the body of the sphenoid bone. 



In the frontal section shown in fig. 20 we have represented 

 the manner of constriction of the superior and dorsal portions of 

 the nasal fossae in the formation of sphenoidal-sinus anlages. 

 Later the sinuses are represented by very shallow pits and by 

 the 5th month of extrauterine life the sinuses are well estab- 

 lished (fig. 42). 



V Some Later Developmental Changes on the Lateral 

 Wall as Presented in the Adult Nose 



It is not necessary to consider the adult lateral nasal wall in 

 detail since the general anatomy is so well known, and besides 

 the descriptions of the late fetal conditions as given, would in a 

 measure be duplicated in a detailed description of the adult lateral 

 wall. There are, however, certain conditions and relations of 

 great importance which develop much later, and varying opinions 

 are entertained on some of these points. We will, therefore, in 

 subsequent paragraphs consider the later developmental changes 

 with especial reference to: (1) the number of ethmoidal conchae 

 in the adult; (2) the ethmoid cells with especial reference to their 

 ostia; (3) the ostia maxillaria; (4) the relations of the nasofrontal 

 duct with especial reference to the manner of communication of 

 the frontal sinus with the meatus nasi medius. 



The number of ethmoidal conchae in the adult 



In previous paragraphs we dwelt at some length on the num- 

 ber of ethmoidal conchae that are differentiated before birth. 

 We found that the number varied from three to five; with four 

 major conchal folds in the ethmoidal region rather common, and 

 five not at all unusual. The concha suprema III early loses its 

 identity in the vast majority of cases. This is also true of the 

 concha suprema II; however it is as a rule somewhat farther 



Journal op Morphology, Vol. 21, No. 4. 



