24 THE STRUCTURE OF THE FOWL 



depression in which are several openings. The 

 largest of these leads into the tympanic cavity, 

 and the most inferior of them forms the entrance 

 to the carotid canal. The other end of the canal 

 is on the base of the skull at a short distance 

 from the middle line. Within the tympanic 

 cavity are several openings, three of which are 

 of importance. Two of these are about the 

 middle of the cavity. The upper one is the 

 fenestra vestibuli into which the end of the 

 columella fits. The lower is the fenestra 

 cochlece. From the lower and anterior part 

 of the tympanic cavity a funnel-shaped de- 

 pression leads into the bony auditive or 

 Eustachian tube, the other end of which is a 

 small opening close to the middle line and about 

 the same level as the anterior opening of the 

 carotid canal. 



The foramen of exit for the fifth cerebral 

 nerve is immediately below the concavity in 

 the temporal bone with which the quadrate 

 articulates. The small openings by which the 

 third and fourth cerebral nerves leave the 

 cranium are immediately lateral to the optic 

 foramen, with which they not infrequently 

 blend. The first cerebral or olfactory nerves 

 leave the cranium by an opening in the middle 



