The Sinus Maxillaris in Man. 325 
a slit-like shape at the side of the nose (fig. 4). It has its greatest 
measurement in the ventrodorsal direction, while mediolaterally 
the cavity occupies comparatively little space. In embryos aged 
from 100 to 105 days the ventrodorsal measurement is about 2 
mm. (fig.2). In a120-day embryo the distance is about 2.5 mm. 
(figs. 3 and5 A). Ina 100-day embryo the most ventral spur of 
the sinus is about 6.5 mm., and the most dorsal spur 8.5 mm. 
from the tip of the nose. 
It will be remembered that, in the embryo, the processus 
alveolaris of the maxilla is in proximity to the orbit, and when 
we recall the fact that the unerupted teeth are contained in this 
situation, it at once becomes evident that the sinus maxillaris 
must be correspondingly small at this time. Because of these facts 
the sinus of a 7-month fetus measures only 5 mm. in the ventro- 
dorsal plane, while that of a fetus at term has increased this 
distance to approximately 7 mm. (fig. 5 B). During the latter 
month of intrauterine life the sinus gains in the mediolateral 
plane, so that at term this distance measures from 3 to 4 mm. 
It is generally stated that the deciduous teeth hold the sinus 
maxillaris in check, and that the cavity rapidly assumes larger 
dimensions as the first dentition progresses. I, however, find 
that the growth of the sinus is rather uniform, and that the first 
dentition has little to do with any rapid increase in the size of the 
eavity. The age of the child and the size of the sinus, apparently, 
progress pari passu (fig. 6). 
The ventrodorsal measurement of the sinus in a child aged 
6 months is 10 mm., but the cavity has not developed sufficiently 
in the mediolateral plane to reach beneath the orbit. In a child of 
9 months the ventrodorsal distance is 14 mm., with a superoin- 
ferior measurement of 5mm. At the end of the first year the sinus 
has reached a ventrodorsal measurement of 16 mm., a superoin- 
ferior of 6 mm.; and has now reached a mediolateral point suffh- 
cient to pass beneath the orbit. As the maxilla grows, the sinus 
remains for some time on the medial side of the infraorbital 
canal (fig. 10). By the twentieth month the sinus measures 
ventrodorsally 20 mm. (fig. 5) and has, as a rule, extended above 
the rudimentary first permanent molar tooth. 3 
