The Sinus Maxillaris in Man. 339 
positive group fall, however, into a very important class of speci- 
mens. That these crescentic projections offer, at times, almost 
insuperable obstruction in attempting to drain fluid from the 
sinus through an opening either in the processus alveolaris, or in 
the meatus nasi inferior, is a fact that we should be cognizant 
of. This was repeatedly demonstrated by first filling the sinus 
with a liquid, then making an opening at some point on the 
processus alveolaris; thus draining out what would come away. 
If some of the fluid was retained—allowing for adherence to 
mucous membrane—the facial or anterior surface of the maxilla 
was removed to find where the remaining fluid was lodged. As 
a rule the portion of fluid was retained by a recess or recesses on 
one or more of the sinus walls. At other times a second and 
even a third opening was made, either through the alveolar 
border or -through the meatus nasi inferior, before the remain- 
ing fluid would come away. If after repeated attempts the fluid 
could not be located, the ventral wall of the cavity was removed 
to ascertain the reason for its retention, and the fact was thus 
demonstrated that repeated punctures, in some cases, would not 
reach all of the recesses. 
Just what these recesses mean in all cases is difficult to say. 
Some of them are of course formed by elevations caused by tooth 
fangs, but these as a rule are of minor importance and only 
occasionally form deep recesses. Others are formed by projec- 
tions of mucous membrane, which may or may not be caused 
by ecrescentic bone projections. Where complete septa exist, the 
sinus maxillaris very likely developed from two primary pouches. 
In some cases the intervening wall may have disappeared in 
part, thus leaving the larger crescentic projections which occa- 
sionally are found in the adult sinus. A double pouching of the 
primitive sinus maxillaris was mentioned in a previous para- 
graph on the development of the cavity. Unequal resorption 
of the bone during the growth of the sinus is doubtless a cause 
for some projections occurring on the walls of the cavity. 
