FKONTAL SECTIONS OF THE CEANIUM. 



187 



meatus below, is seen with the middle concha medial to it, and the anterior ethmoidal 

 cells to its lateral side above. If the section passes through the canal for the naso- 

 lacrimal duct the continuity of that channel leading from the orbit above to the inferior 

 meatus of the nose below is clearly shown. Its medial wall above, by which it is separated 

 from the cavity of the nose, is formed by the thin lacrimal bone ; below, it passes under 

 cover of the inferior concha to open into the anterior part of the inferior meatus. It is 



FIG. 175. PART OF THE FRONTAL, NASAL, AND MAXILLARY BONES REMOVED IN ORDER TO 

 DISPLAY THE RELATION OP THE VARIOUS CAVITIES EXPOSED. 



The frontal and maxillary bones, where cut, are coloured blue ; the ethmoid and the inferior concha red ; 



the lacrimal and vomer yellow. 



1. Frontal sinus. 



2. Septum of frontal sinus deflected towards the right. 



3. Infundibulum leading from sinus to middle meatus. 



4. Anterior ethmoidal air-sinuses. 



5. Middle concha. 



6. Eed line in upper part of osseous canal for naso- 



lacrimal duct, laid open throughout its entire 

 length on the right side. 



7. Cavity of maxillary sinus laid open. 



8. Middle meatus of nose. 



9. Inferior meatus of nose. 



10. Inferior concha. 



11. Nasal septum. 



12. Canal for naso-lacrimal duct laid open through- 



out its entire length. 



13. Anterior nasal spine. 



separated from the maxillary sinus laterally by a thin lamina of bone. The cavity of 

 the maxillary sinus is seen to extend upwards and forwards so as to pass over the lateral 

 side as well as slightly in front of the canal for the naso-lacrimal duct. 



The lower margins of the middle conchae lie pretty nearly on a level with the 

 most dependent parts of the orbital margins, whilst the lower borders of the inferior 

 conchse are placed a little above the lower margin of the piriform opening on a level 

 with the lowest point of the zygomatico-maxillary suture. 



Such a section will reveal any deflection of the nasal septum should it exist, and will 

 also show that but a narrow cleft separates the upper part of the septum, on either side, 

 from the medial surface of the superior conchee. 



The next section (Fig. 176) passes through the anterior part of the temporal fossa just 



