636 Jacob Parsons Schaeffer. 



to form very shallow recesses superior and inferior to it, and occa- 

 sionally it has been mistaken for the superior nasal concha (fig. 

 19). From the superior and inferior recesses, and from the 

 ventral and superior extremity of the superior meatus, most of 

 the posterior group of ethmoidal cells develop — a matter which 

 will be taken up subsequently. Frequently a posterior ethmoid 

 cell develops from the meatus nasi suprema I. The latter meatus, 

 however, is present in only 62.5 per cent of my adult specimens 



The early changes in the superior and dorsal portion of 



the nasal fossae 



A frontal section through the dorsal portion of the nasal cavity 

 in a three-months embryo will already indicate the manner of 

 constriction of a portion of the dorsal and superior part of the 

 nasal fossae in the formation of the early anlages of the sinus 

 sphenoidales. In a 120-day embryo the sphenoidal-sinus anlages 

 are well advanced, but have not reached, or at least not extended 

 into, the body of the developing sphenoid bone. The lateral 

 nasal plates of cartilage more or less overhang the sphenoidal- 

 sinus anlages (fig. 20). 



The number of ethmoidal conchae and meatuses that are 

 differentiated before birth 



As to the number of ethmoidal conchae and meatuses that are 

 differentiated during the latter months of intrauterine life con- 

 flicting opinions are held. The meatus inferior and the concha 

 inferior are constant, hence they will not be considered in the pres- 

 ent connection. 



Zuckerkandl states that three and at the highest four ethmoidal 

 meatuses are formed (including the meatus medius) . This would 

 indicate three and at the highest four ethmoidal conchae. In 

 reference to the latter hesays: ''Drei Siebbeinmuschelnreprasen- 

 tieren . . , die typische Faltungsweise des Siebbeines." 

 Killian, whose researches on this point are extensive, states that in 

 fetuses of the ninth to the tenth month, five and even six eth- 



