318 Jacob Parsons Schaeffer. 
According to my observations the earliest evidences of maxil- 
lary pouching are found about the seventieth day of fetal life. Kal- 
lius places the time of the primary evagination. during the 
middle of the third month, ‘‘Die Oberkieferhohle erscheint in 
der Mitte des 3. Monats.”’ J. Kollman places the time of pouch- 
ing later, ‘‘Seine Anlage beginnt erst bei Foeten Von 8 cm. 
Linge.’’ Gegenbaur quotes Dursy as authority for the following: 
Schon bei 8 em. lange Embryonen buchtet sich der Raum der Nasen- 
hdhle zwischen mittlerer und unterer Muschel gegen den hier verdickten 
Knorpel der Seitenwand der Nasenhohle aus und bildet die Anlage des 
Sinus Maxillaris. 
I have found the primitive maxillary pouch duplicated, 1. e., 
two pouches growing laterally side by side. (This may explain 
some of the duplications of the adult ostium maxillare—the two 
primary pouches fusing distally, leaving the two points of evagi- 
nation as the ostia maxillaria of the adult sinus. Other duplica- 
tions of the adult ostium may be caused in a manner similar 
to the formation of the accessory ostium). 
This embryonal condition probably explains some of the cases 
in which the sinus maxillaris is divided into two partially or 
wholly separate compartments by a vertical partition, i. e., each 
pouch developing into an adult cavity independent of its mate 
(see subsequent paragraph). 
The primary ostium maxillare varies greatly in its dimensions 
in different embryos (figs. 2, 3). This is entirely in accord with 
adult conditions, since the ostium of the adult sinus has a great 
range of dimensions (table D). The great differences in the 
dimensions of the ostium may be due to early fusion of two or 
more primary maxillary pouches; or the primitive pouching 
may have been single but extensive, as is frequently the case. 
These two latter would give rise to long slit-like ostia, while the 
single and less extensive pouching would give us the typically 
shaped and average sized adult ostium. : 
Sometime prior to the establishment of the maxillary pouch? 
7 It is indeed difficult, in some cases, to say which structure is the primary one 
in establishing an Anlage. It most cases the processus uncinatus is the first to 
