632 Jacob Parsons Schaeffer. 



frontal sections (fig. 11). This, however, does not detract from 

 the statement that the groove between the ethmoidal amd maxil- 

 lary folds is present, at least to some extent, before the folds have 

 gained any appreciable bulging. Later we have a proliferation 

 of the mesenchyme and a deepening of the furrow (primitive 

 meatus nasi medius) inferior to it, hence the ethmoidal fold be- 

 comes more prominent. Gradually in place of the single ethmoidal 

 fold we have, with the increase of the nasal fossa in the dorso- 

 superior direction, the establishment of anlages of the individual 

 ethmoidal conchae — this, as a rule, taking place in order from the 

 most caudal to the most cephalic ethmoidal concha (figs. 13, 14, 

 15, and 21). 



As may be inferred from the above, the ethmoidal region on each 

 side presents but for a brief time a single fold (fig. 13). As the 

 nasal fossa enlarges superiorly and dorsally there is a differen- 

 tiation in this region into two folds (fig. 14) — this change occur- 

 ring approximately from the forty-eighth to the fiftieth day of 

 fetal life. A later stage, 95 to 100 days, shows three well formed 

 ethmoidal conchae (fig. 15). By the fourth month of fetal life 

 the conchal field shows from three to four ethmoidal conchae, 

 besides the concha inferior. Fetuses from the seventh month to 

 term will, if carefully examined, show from three to jive ethmoidal 

 conchae (figs. 21 and 30). Of course in each case a corresponding 

 number of furrows or meatuses are established — some of the meat- 

 uses, however, being very rudimentary. After birth the ethmoidal 

 conchae and meatuses become reduced in number. This reduc- 

 tion is not carried so far in some cases as in others — thus account- 

 ing for the supernumerary or additional conchae and meatuses of 

 many adult noses. Doubtless the number of ethmoidal conchae 

 that are differentiated before birth have an important bearing on 

 the number of conchae that maybe present in an individual case— 

 this is probably just as important a factor in determining the num- 

 ber of adult ethmoidal conchae as is the retrogressive change of 

 reduction. 



