692 Jacob Parsons Schaeffer. 



adult cavities. On the base or medial wall of the cavity we have 

 an area that is in time composed of merely two layers of abutting 

 mucous membrane, one the mucous membrane of the middle 

 meatus, and the other the mucous membrane of the maxillary 

 sinus. These two layers of mucous membrane with no interven- 

 ing bone offers very little resistance to the growing maxillary cav- 

 ity. In time they become so thinned out and attenuated in many 

 instances that ultimately an opening is formed, thus establishing 

 the ostium maxillare accessorium. This reminds one of the early 

 thinning and attenuation and ultimate rupture of the two layers 

 of abutting epithelium — the bucconasal membranes — in the es- 

 tablishment of the primitive choanae. 



If we accept this view, and to me it seems plausible, as to the 

 genesis of the ostium maxillare accessorium, we would not expect 

 to find the ostium in fetuses nor in young children. We would 

 neither expect to find this accessory aperture often in the young 

 adult, i.e., before the twentieth year of age. We would, however, 

 especially look for it in the more advanced adult, after the walls 

 of the sinus maxillaris have been thinned out by the large adult 

 cavity. This is in accord with my results. I have never been able 

 to find the ostium maxillare accessorium in the fetus nor in the 

 child. It occurs, as far as my observations would indicate, only 

 in the adult. I have found it in adults between the ages of twenty 

 and ninety years. It is a very frequent aperture from thirty-five 

 years on. Symington likewise never found the accessory ostium 

 in children. He says: ''In children I have never found more than 

 one aperture, viz., that into the infundibulum." 



I have, therefore, come to the conclusion that the ostium maxi- 

 lare accessorium is in most instances established by the develop- 

 ing sinus maxillaris. The growth of the sinus causes the tw^o layers 

 of abutting mucous membrane to become thinned out and atten- 

 uated, ultimately resulting in an opening in very many adult noses. 

 Some are doubtless due to a pathological process, and others 

 produced in a mechanical manner by septal spurs. Enlarged mid- 

 dle conchae may also wear holes into the maxillary sinus in this 

 position; this is, however, rare. 



