THE FACE. 



13 



towards the cavity, and often defective in part. The nerve will best be avoided by 

 not directing the perforation too much forwards. Between the semicircular canal 

 in front and the lateral sinus behind, the air-spaces are in relation internally with the 

 posterior fossa of the base of the skull, the thickness of the intervening bone ranging 

 from 1 to 9 mm. The original perforation must be kept below the supramastoid crest 

 in order to avoid opening the middle fossa of the skull ; and it should not extend 





mastoid foramen. 



aperture into 

 mastoid antrum. 



Fig. 9. LOWER AND HINDER PART OF SKULL, IN WHICH AN OPENING HAS BHEN MADE INTO THE 



MASTOID ANTRUM, AND ON WHICH THE COURSE OF THE OCCIPITAL ARTERY AND LATERAL SINUS 



ARE INDICATED. ( From a photograph by G. W. B. Waters.) f (G. D. T.) 



backwards more than 2 mm. beyond the posterior boundary of the suprameatal 

 triangle, or the lateral sinus may be endangered. 



In the infant and child the mastoid antrum has nearly its full size, but its outer 

 wall is relatively thin. The mastoid cells are, however, not usually developed before 

 twelve years of age. 



The face. In the face proper, the nasal bones and the margin of the anterior 

 nasal aperture are readily traced, and at the lower part of the latter, in the root of 

 the septum narium, the anterior nasal spine is felt. In front of this opening the form 

 of the upper and lower lateral cartilages can be distinguished, and the inner portion 

 of the latter is more clearly made out by passing the finger into the nostril, by which 

 means part of the cartilage of the septum, the lower margin of the upper lateral 

 cartilage, and sometimes the tip of the inferior turbinate bone, can also be felt. 



With the nasal speculum, if the parts be normal, the dull red mucous membrane 

 of the floor of the nose and of the lower part of the septum may be seen, the brighter 

 red inferior turbinate body for the greater part of or all its extent, and the inferior 

 meatus for a variable distance. The anterior border and a small part of the inferior 

 border, i.e., the operculum, of the middle turbinate body may also be seen, and a 

 very small part of the middle meatus. The fore part of the roof is visible, but the 

 superior turbinate body rarely, and the superior meatus never. The back of the 

 pharynx can be seen in a nose of moderate dimensions. 



Below the base of the zygoma, the temporo-maxillary articulation is quite super- 



