998 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



The Accessory Sinuses of the Nose (Sinus Paranasales) (Figs. 855, 856, 859). 



The accessory sinuses or air cells of the nose are the frontal, ethmoidal, sphe- 

 noidal, and maxillary; they vary in size and form in different individuals, and 

 are lined by ciliated mucous membrane directly continuous with that of the nasal 

 cavities. 



The Frontal Sinuses (sinus frontales), situated behind the superciliary arches, 

 are rarely symmetrical, and the septum between them frequently deviates to one 

 or other side of the middle line. Their average measurements are as folfrnvs: 

 height, 3 cm.; breadth, 2.5 cm.; depth from before backward, 2.5 cm. Each opens 

 into the anterior part of the corresponding middle meatus of the nose through the 

 frontonasal duct which traverses the anterior part of the labyrinth of the ethmoid. 

 Absent at birth, they are generally fairly well developed between the seventh and 

 eighth years, but only reach their full size after puberty. 



Superior concha 



Ethmoidal air cell 



Superior 

 meatus 



Middle 

 concha 



Middle 

 meatus 



Septum 



nasi 

 Inferior 

 concha 

 Maxillary 



sinus 

 Inferior 

 meatus 



FIG. 859. Coronal section of nasal cavities. 



The Ethmoidal Air Cells (cellules ethmoidales) consist of numerous thin-walled 

 cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, 

 lacrimal, sphenoidal, and palatine. They lie between the upper parts of the nasal 

 cavities and the orbits, and are separated from these cavities by thin bony 

 laminae. On either side they are arranged in three groups, anterior, middle, and 

 posterior. The anterior and middle groups open into the middle meatus of the 

 nose, the former by way of the infundibulum, the latter on or above the bulla 

 ethmoidalis. The posterior cells open into the superior meatus under cover of 

 the superior nasal concha; sometimes one or more opens into the sphenoidal sinus. 

 The ethmoidal cells begin to develop during fetal life. 



The Sphenoidal Sinuses (sinus sphenoidales) contained within the body of the 

 sphenoid vary in size and shape; owing to the lateral displacement of the inter- 



