THE SKULL 37» 



end of which is attached to the tympanic 

 membrane. 

 /3. The posterior opening of the Eustachian tube 



is a funnel-Hke depression, at the ventral 

 and anterior corner 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 line. 



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

 behind forwards. 



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. 



8. The posterior tympanic recess is a large 



depression, close to the dorsal border of the 



tympanic cavity, and just above the fenes- 



tral 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 skuU, below 



and in front of the articular surface for the 



quadrate. 



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



of the skull, which lodges the eyeball : it is 



bounded above by the frontal bone ; in front. 



