THE SKULL. 413 



and a lower, the fenestra rotunda. The 



former of these lodges during life the inner 

 end of the auditory ossicle or columella, a 

 slender bar of bone and cartilage, the outer 

 end of which is attached to the tympanic 

 membrane. 



6. The posterior opening of the Eustachian canal 



is a funnel-like 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 basi-sphenoid, to open, as already seen, 

 on the base of the skull, close to the middle 

 line. 



Pass a bristle along the Eustachian canal of one side, 

 from behind forwards. 



y. The anterior tympanic recess is a slit-like 

 depression, immediately above the posterior 

 opening of the Eustachian canal, with which 

 it is often confluent. 



S. The posterior tympanic recess is a large 

 depression close to the dorsal border of the 

 tympanic cavity, and just above the fene- 

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

 process of the frontal bone. 



iii. The articular surface for the quadrate is a de- 

 pression 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 



