20 ANATOMY OF A CHELONIAN. 



seen to communicate with an outer division 

 by means of a narrow passage, through which 

 the cotumella auris (now exposed in situ) passes 

 from the tympanic membrane on its way to 

 Xh& fenestra ovalis. 



e. Just outside the cartilaginous plate referred to 

 above and close behind the quadrate is a fora- 

 men for the entry of the carotid artery, which, 

 within the bone, divides into an internal carotid, 

 which enters the skull cavity, and an external 

 carotid, which emerges by the foramen on the 

 roof of the skull mentioned above (25, e). 



f. In front of the cartilage, and nearer its outer 

 than its inner side, is a small aperture which 

 leads into a canal which passes forward some 

 way in the bone forming the base of the skull. 

 Into it one division of the anterior extrernity 

 of the sympathetic nerve will subsequently 

 (199) be found to pass. 



g. External to the aperture of the sympathetic 

 channel, and in front of the aperture of the 

 carotid canal, is the small foramen of exit for 

 the seventh cranial nerve (200). 



27. On the Side of the Skull, note : 



a. The large ear-opening leading into the external 

 division of the tympanum, which reaches back 

 into the post-auditory process. Close to the 

 outer side of the proximal end of the quadrate 

 bone is the narrow passage through which the 

 columella passes on to the inner expansion of 

 the tympanic cavity. 



b. Farther forward is the temporal fossa covered 



