614 Jacob Parsons Schaeffer. 



I Introduction 



A survey of the literature on the lateral wall of the cavum 

 nasi indicates that commendable researches have been carried 

 out by different investigators. Although much careful work 

 has been done, conflicting opinions are held on some points of 

 the development and the gross anatomy of this portion of the 

 olfactory organ. The idea of an unvarying typical form in the 

 gross anatomy of the structures and relations in this region of 

 the nose seems too much in evidence in some of the general text- 

 books of anatomy. In fact the exceptioiis in some instances 

 to the descriptions given are so numerous that the exception is 

 described rather than the average condition. This is especially 

 true in the manner of communication of the nasofrontal duct 

 with the middle nasal meatus. The ostium maxillare accesso- 

 rium — a very common aperture indeed — does not receive the 

 recognition it should have. According to my series of speci- 

 mens, 62.5 per cent of ethmoidal regions possess in the adult 

 three conchae. Books generally describe and picture two eth- 

 moidal conchae as the typical number, and apparently would 

 have us think that three ethmoidal conchae are rather excep- 

 tional. 



In order to determine whether the embryology would account 

 for the varied adult conditions one meets, I undertook the study 

 of the various developmental stages in the formation of the com- 

 plex lateral nasal wall. It was deemed essential that the embry- 

 ological stages in the formation of the nasal cavity be consid- 

 ered before taking up for detailed study its lateral wall. The 

 paper will, therefore, include: (1) a brief description of the 

 developmental stages of the nasal fossae; (2) the detailed embry- 

 ology of the lateral walls of the nasal fossae ; (3) the gross anatomy 

 of the lateral walls as presented in the term fetus and the young 

 child; (4) the adult lateral walls with especial reference to some 

 later developmental changes. 



It is obvious that the fundamental structures to be considered 

 in a study of the development of the lateral wall of the cavum nasi 



