SENSE OF HEARING. 225 



The stapedius muscle emerges from the cavity of a pyramid of bone 

 projecting from the posterior wall of the tympanum; the tendon passes for- 

 ward, and is inserted into the neck of the stapes bone, posteriorly, near its 

 point of articulation with the incus. 



The laxator tympani muscle, so called, is now generally regarded as being 

 ligamentous in nature, and not muscular. 



FIG. 36. TYMPANUM AND AUDITORY OSSICLES (LEFT) MAGNIFIED. 

 A.G. External meatus. M. Membrana tympani, which is attached to the handle 



ive 



and must be imagined to penetrate the plane of the paper, t. Line of traction of 

 the tensor tympani. The other arrows indicate the movement of the ossicles when 

 the tensor contracts. 



The Eustachian tube, by means of which a free communication is estab- 

 lished between the middle ear and the pharynx, is partly bony and partly 

 cartilaginous in structure. It measures about ij inches in length; com- 

 mencing at its opening into the nasopharynx, it passes upward and outward 

 to the spine of the sphenoid bone, at which point it becomes somewhat con- 

 tracted; the tube then dilates as it passes backward into the middle-ear cavity; 

 it is lined by mucous membrane, which is continued into the middle ear and 

 mastoid cells. 



