EXTERNAL MEATUS 



547 



the anterior angle of the petrous part of the temporal bone. When the 

 dissection ifc properly done the greater part of the temporal bone is removed 

 from the remainder of the skull, with the cartilaginous part of the auditory 

 tube attached to the anterior angle of its petrous portion, and a small part 

 of the body of the sphenoid bone attached to its apex. The anterior wall 

 of the mandibular fossa was separated by the first saw cut, and the posterior 

 wall is exposed, with the cartilaginous part of the auditory tube attached to 

 its medial end and the cartilaginous part of the external acustic meatus to 

 its lateral border. The dissector should now cut away the tragus of the 

 auricle, to expose the orifice of the external meatus which lies at the bottom 

 of the concha ; then, with knife or scissors, he must remove the anterior 



Tympanic antrum Canalis facialis 



Pyramid 



Apertura 



tympanica 



canaliculi 



chordae 



Groove for 



membrana 



tympani 



Cochlea 



Canal for tympanic nerve 



FIG. 232. Frontal section of the Right Temporal Bone passing through the 

 external and the internal acustic meatuses. 



wall of the cartilaginous part of the external meatus. Next pass a probe 

 into the bony part of the meatus to gauge its length, and, whilst the probe 

 is kept in position as a guide, cut away the anterior wall of the bony 

 part of the meatus, taking care not to injure the tympanic membrane which 

 closes the medial end of the meatus. When the dissection is completed the 

 boundaries of the meatus and the outer surface of the tympanic membrane 

 should be examined. 



Meatus Acusticus Extenms. The external acustic meatus 

 runs anteriorly and medially from its lateral orifice to its 

 medial boundary, and, during its course, it forms a slight curve 

 with the convexity upwards. Its total length, measured from 

 the bottom of the concha to the tympanic membrane, is about 



