Lateral Wall of the Cavum Nasi in Man. 623 



respectively. Kolliker places the time of establishment of the 

 primitive choanse ''in der zweiten Halfte des zweiten Monates." 

 The apparent discrepancy in the time at which the bucconasal 

 membranes rupture is doubtless due to different methods of 

 determining the age of embryos. 



As a result of the rupture of the bucconasal membranes we have 

 established two openings — the primitive choanae (primitive 

 Gaumenspalten, Dursy; innere Nasengange, innere Nasenlocher, 

 Kolliker). There is thus established in man for a second time 

 a commnication between the oral and the nasal fossae. The 

 hitherto blindly ending nasal fossae now communicate not only 

 with the exterior by means of the nares, but also with the mouth 

 cavity by means of the primitive choanse. 



Epithelial plugs in the nares 



When first formed the nares communicate freely with the ex- 

 terior, but shortly afterwards, say about the fortieth day of em- 

 bryonal life, the lumina of the nares in very many cases become 

 filled in with epithelial plugs (figs. 6 and 7). This plugging which 

 is due to a proliferation of the epithelial cells, seems to take 

 place some time after the fusion of the medial and lateral nasal 

 processes. In some cases the plugging is absolute, and in others 

 deviating passages through the plugs may be seen. Sometimes 

 the plugs are more or less fenestrated. I find plugging rather 

 frequent from the fortieth to the sixtieth day. I have, however, 

 seen it in a 120-day embryo. The passages (nares) are apparently 

 later opened by a shedding of the epithelial plugs rather than by 

 a resorption of the cells — probably both factors are involved. 

 As evidence of a shedding of the epithelial plugs we frequently 

 find shreds of epithelial masses extruding from the nares. 



The primitive palate 



With the formation of the primitive choanae we have also 

 established the primitive palate, i.e., the portion of the roof of the 

 oral fossa extending from the primitive choanae to the nares. 



