674 Jacob Parsons Schaeffer. 



however, matters very little what interpretation we place here — 

 probably both factors are more or less involved — the fact remains 

 that from these preexisting furrows and recesses the accessory 

 air spaces develop. This is true of all the paranasal chambers 

 with the single exception of the sphenoidal sinus, which is at 

 first, as former writers have pointed out, nothing but a constric- 

 tion from the dorsal and superior portion of the nasal fossa. Of 

 course the factors of growth ( of the sac) and resorption (of sur- 

 I'ounding tissue) are early brought into play (fig. 20). 



The sinus maxiUaris 



The sinus maxillaris is primitively merely a pouching or evagin- 

 ation of the mucous membrane of the infundibulum ethmoidale. 

 This pouching is very evident about the seventieth day of fetal 

 life, and is best shown by reconstructing the infundibulum eth- 

 moidale. The earliest changes in its anlage-formation are so 

 slight that they are difficult of appreciation by an examination 

 of serial sections only. The anlage of the sinus maxillaris is 

 usually represented by a single pouch, but, as I stated in a pre- 

 vious paper, we sometimes find two pouches growing side by 

 side from the infundibulum ethmoidale. Again the pouching 

 may be very extensive, and in these cases it is indeed hard to 

 say where the infundibulum ethmoidale ends and where the 

 anlage of the sinus maxillaris begins. In such cases the infundibu- 

 lum ethmoidale is in a sense a part of the sinus maxillaris. Sey- 

 del makes the general statement that ' ' der Raum des Infundibu- 

 lum, der zwischen Processus uncinatus und Orbitalwand liegt, 

 ist als ein Theil des Sinus (sinus maxillaris) zu beurtheilen." If 

 we accept the above interpretation then the sinus-maxillaris 

 anlage is established with the first evidences of the infundibulum 

 ethmoidale. Zuckerkandl also, presumably, considers the infundi- 

 bulum ethmoidale a part of the early sinus maxillaris. What 

 he labels ''S.m." (Sinus maxillaris), (Tafel XI, Figs. 5, 6, Normale 

 und pathologische Anatomie der Nasenhohle und ihrer pneu- 

 matischen Anhiinge, Ed. I, Wien und Leipzig, 1893) is certainly 

 in part infundibulum ethmoidale. We seldom see the primitive 



