Lateral Wall of the Cavum Nasi in Man. 



639 



sionally some specimens show a low degree of differentiation and 

 possess but three ethmoidal conchae (fig. 28). 



It is indeed difficult to say whether in the latter cases the pro- 

 gressive changes (differentiation) have not been carried so far as in 

 some others, or whether retrogressive changes (coalescence of two 

 or more conchae with obliteration of the intervening furrows) 



Septum nasi. 



Concha iiasaiis 

 siiprcina / 



Recenmix superior 

 CiHirlirt /ui.ialix 

 auprrtor 



(Vjnr/ift acreMoria 



:^ Crista xtiprema 



Reeemas inferior 



Cottrbtt tiomilifi 

 media 



Concha nasali» 

 inferior 



Meatus nasi 

 inferior 



Fig. 19 (X 10) Outline drawing of a frontal section through the nose of the 

 same embryo as those in figs. 17 and 18. This section (slide 67) is in the region of 

 the accessory concha of the meatus nasi superior, hence is farther dorsal than 

 that in fig. 17. 



Shows how the crista suprema of the concha media aids in forming the recessus 

 inferior of the meatus superior. Compare the meatus superior of this section 

 with the meatus medius of section,, fig. 18. 



took place at an earlier time. The latter is doubtless an active 

 process after birth, because we rarely find more than three eth- 

 moidal conchae. in the adult. It is, therefore, quite possible that 

 retrogressive changes are instituted much earlier in some cases, 

 and that the ethmoidal regions which have a comparatively small 

 number of conchae in the late fetus, originally possessed a larger 

 number of folds. I, however, believe that in the majority of these 



