Chap. VI J NOSE AND NASAL CAVITIES. 9! 



from above downwards and backwards. Into this 

 groove (the infundibulum) open the frontal sinus, the 

 anterior ethmoid cells, and the antrum. The aperture 

 of the frontal sinus appears as a small round hole at 

 the upper and anterior end of the groove. The 

 ethmoid cells open a little way lower down on the 

 groove, while the antrum has its orifice at the hinder 

 part of the infundibulum. This orifice is slit-like, is 

 about the centre of the middle meatus, and is nearly 

 one inch above the floor of the nasal fossae. The 

 orifice is nearer to the roof than the floor of the 

 antrum, and thus no facility is offered for the escape 

 of accumulated fluids. 



The middle turbinated bone is high up. Its highest 

 point (its anterior extremity) is nearly on a level with 

 the tendo oculi. 



Rhinolithes (stone-like masses of calcareous matter, 

 formed, as a rule, around foreign substances) are most 

 often found in the inferior meatus. 



The width of the nasal floor is about half an inch, 

 or a little over. Its smooth surface greatly favours 

 the passage of instruments. It presents a gentle slope 

 from before backwards. At its anterior part is a 

 depression of mucous membrane over the incisor 

 foramen. This foramen is a vestige of the great com- 

 munication that once existed between the cavities of 

 the nose and mouth. 



The mucous membrane lining the nasal cavi- 

 ties varies in parts. It is very thick and vascular 

 over the turbinate bones and over the lower two- 

 thirds of the septum, while over the nasal floor, and in 

 the intervals between the turbinate bones, it is very 

 much thinner. The mucous membrane lining the 

 various sinuses and the antrum is conspicuously thin 

 and pale. The membrane is provided with many 

 glands, which are most conspicuous over the lower and 

 hinder parts of the outer wall and over the posterior 



