THE CELLULE ETHMOIDALES 77 



CELLUUE ETHMOIDALES POSTERIOR 



The cellulse ethmoidales posterior vary in number from 

 one to five on each side, the general average in 202 lateral 

 nasal walls being 2.62. The origin of the posterior cells was 

 found to be as follows: 



81.1 per cent, from the meatus superior 

 18.4 " " " " " supremusl 



0.5 " " " " " " II 



The ostia of the cells vary from oval openings 0.5 mm. to 

 3 mm. in diameter, to slit-like openings from 3 to 14 mm. 

 long and from 1 to 3 mm. wide. The most constant loca- 

 tion for an ostium is at the anterolateral extremity of the 

 meatus superior. In only one instance was a superior meatus 

 found which contained no ostium for an ethmoidal cell. In 

 that case posterior ethmoidal pneumatization was entirely 

 from the meatus supremus I. 



The extent of pneumatization shows marked variations. 

 Posterior cells often extend for variable distances into the 

 supra-orbital plate of the frontal bone, into the orbital proc- 

 ess of the palate bone, into the infra-orbital plate of the 

 maxilla, and in rare instances may invade the body of the 

 maxilla, forming, when the pneumatization is extensive, 

 what has been termed a double maxillary sinus. Fig. 50 

 shows an aberrant cell which had its origin in the superior 

 meatus, invading the posterosuperior portion of the maxilla, 

 but the invasion in this case is not sufficient to justify its 

 classification as a double maxillary sinus. 



The most posterior ethmoidal cell frequently develops 

 dorsally until a portion of it lies superior to the ventral por- 

 tion of the sinus sphenoidalis, but in no case was there a 



