THE SKULL 367 



end of which is attached to the tympanic 

 membrane. 

 p. The posterior opening of the Eustachian tube 

 is a fannel-like depression, at the ventral 

 and anterior comer of the tympanic cavity. 

 The tube into which it leads passes forwards 

 and inwards, between the basi-temporal and 

 the true base of the cranium, to open, as 

 already seen, at the base of the skuU, close 

 to the middle Une. 



Pass a bristle along the Eustachian tube of one side, from 

 behind forwa/rds. 



y. The anterior tympanic recess is a slit-like 

 depression, immediately above the posterior 

 opening of the Eustachian tube, with which 

 it is often continuous. 



B. The posterior tympanic recess is a large 

 depression, close to the dorsal border of the 

 tympanic cavity, and just above the fenestral 

 recess. 



ii. The zygomatic process of the squamosal is a 

 thin bar of bone, which projects forwards 

 almost horizontally from the anterior and 

 upper edge of the tympanic cavity. Its distal 

 end meets, and often fuses with, the post-orbital 

 process of the frontal bone. 



iii. The articular surface for the quadrate is a 

 depression on the side of the skull, immediately 

 in front of the tympanic cavity, between it and 

 the zygomatic process of the squamosal. 



iv. The foramen of exit for the trigeminal nerve 

 is a round hole in the side of the skull, below 

 and in front of the articular surface for the 

 quadrate. 



v. The orbit is a very large depression in the side 

 of the sknU, which lodges the eyeball : it is 

 bounded above by the frontal bone ; in front. 



