702 Jacob Parsons Schaeffer. 



furrows at times more or less divides the concha into superior and 

 inferior portions. 



25. The sinus paranasales all develop from 'preformed furrows 

 or pits, with the single exception of the sinus sphenoidalis which 

 is primitively nothing but a constriction from the dorsal and supe- 

 rior portion of the nasal fossa. 



26. The sinus maxillaris develops by an evagination from the 

 infundibulum ethmoidale. The primitive sinus may be dupli- 

 cated, in that the pouching is occasionally double. The primitive 

 pouching is at times extensive, including a goodly portion of the 

 infundibulum ethmoidale. These facts doubtless account for the 

 very large ostium maxillare of some adults and the duplication of 

 the ostium maxillare in some cases. 



27. The sinus frontalis may develop either from the frontal 

 recess or from an anterior ethmoidal cell. It may also have a 

 double origin, i.e., from two anterior ethmoidal cells, or from an 

 ethmoidal cell and the frontal recess. Rarely it develops by a 

 direct extension of the' infundibulum ethmoidale. 



28. The anterior group of ethmoidal cells develop from the 

 frontal furrows of the ascending ramus of the middle meatus, and 

 from the furrows found on the lateral wall of the descending ramus 

 of the middle meatus. The infundibulum ethmoidale at its su- 

 perior and ventral termination very frequently dilates into an 

 anterior ethmoidal cell. 



29. The posterior group of ethmoidal cells develop from the 

 superior and ventral end of the superior meatus, from the supe- 

 rior and inferior recesses of the superior meatus, and from the me- 

 atus suprema I. The latter meatus persists in about 62.5 per cent 

 of cases. 



30. We should consider the adult ethmoidal region as usually 

 presenting three conchae rather than two. 



31. In the adult the posterior ethmoidal cells open into the 

 meatus nasi superior and suprema I. The latter meatus is pres- 

 ent in 62.5 per cent of my adult specimens, and in 75 per cent 

 of instances this meatus has a posterior ethmoidal cell communi- 

 cating with it. The superior meatus has in 100 per cent of cases 

 a posterior ethmoid cell communicating with it at its ventral 



