Lateral Wall of the Cavum Nasi in Man. 629 



III The Development of the Lateral Wall of the 



Cavum Nasi 



In the preceding paragraphs we considered the successive 

 stages in the establishment of the nasal cavity, from the thicken- 

 ing of the ectoderm to form the nasal anlage, to the formation of 

 the nasal fossae. We noted the extreme simplicity of the lateral 

 wall of the nasal cavity during the early stages of development. 

 With these considerations on the various developmental stages 

 of the nasal fossae and the early condition of the lateral wall as a 

 basis, we may now to better advantage follow in detail the stages 

 in the formation of the various structures found on the lateral 

 wall. We will, therefore, pass, in order, from the very simple 

 lateral w^all of the early embryo to the complexly configured 

 wall of the term fetus. 



The formation of conchal anlages 



A reference to fig. 2 will indicate the extremely simple lateral 

 wall of the nasal fossa of a 35-day embryo. It will be noticed 

 that there is no evidence of the later complexity and configuration 

 caused by the nasal conchae, the nasal meatuses, the accessory 

 conchae and furrows, and the anlages of the paranasal chambers. 

 In fact the medial or septal wall is more complicated at this time 

 than is the lateral wall — this standing in marked contrast to 

 later conditions (compare figs. 2, 13, 14, and 21). 



Some days later (38- to 40-day embryo) the inferior portion of 

 the lateral wall immediately superior to the primitive palatal 

 processes begins to bulge towards the lumen of the nasal fossa. 

 In fact this bulging for a brief time occupies nearly the whole 

 of the vertical portion of the wall, and approximately the dorsal 

 two-thirds. This fold represents the anlage of the concha nasalis 

 inferior (maxilloturbinal) (fig. 13). Shortly after this (40 to 43 

 days) a second fold appears superior and somewhat dorsal to the 

 first one. The former (ethmoidal fold) is placed in the superior 

 and dorsal angle of the lateral wall. It seems also to extend up on 

 the nasal septum at this point, and some of its prominence is 



