328 



THE RESPIRATORY SYSTEM 



other side of the median plane. The sinus extends backwards 

 into the orbital part of the frontal bone, and lies immediately 

 below the floor of the anterior part of the anterior cranial 

 fossa. On this account, fractures through this part of the 



FIG. 115. Frontal (Coronal) Section through the Skull, showing 

 the nasal fossae. 



a. Inferior concha. 



b. Middle concha. 



c. Superior concha. 



d. Inferior meatus. 



e. Middle meatus. 



f. Maxillary sinus. 



g. Superior meatus. 

 7z. Posterior ethmoidal 



floor of the skull open into the frontal sinus and blood and 

 subdural or even cerebro-spinal fluid may be discharged from 

 the nose. 



The frontal sinus does not appear much before the seventh 

 year. At puberty it can be recognised in X-ray photographs, 

 and it attains its maximum size between the ages of 21 and 25. 



