INTERNAL EAR. 9t 



These bones are maintained in their position by minute 

 ligaments, which unite them to each other and to the sur- 

 rounding walls. Three muscles, also, are in connection 

 with the chain of bones. 



The tensor tympani^ the largest of the three muscles, is 

 contained in an osseous canal, the orifice of which has 

 already been spoken of as lying above that of the Eusta- 

 chian tube. It arises from the walls of this canal, and 

 terminating in a tendon which turns round the processus 

 cochleariformis as a pulley, is inserted into the inner 

 border of the handle of the malleus, at its base. 



The stapedius muscle arises from a canal, in the interior 

 of the pyramid ; it ends in a small tendon which is inserted 

 into the neck of the stapes. 



The laxator tympani arises from the spinous proceSvS of 

 e sphenoid bone, and is continued *by a long tendon 

 rough the fissura vjlaseri, to be inserted into the neck of 

 the malleus, above its long process. 



INTERNAL EAR. 



The INTERNAL EAR, or LABYRINTH, is composed of an 

 osseous and a membranous portion. The osseous labyrinth 

 consists of the vestibule, the semicircular canals, and the 

 cochlea; the membranous labyrinth, of two sacs, called 

 the utricle and the saccule. 



The vestibule is exposed by enlarging the fenestra ovalis. 



The VESTIBULE is an oval-shaped cavity, situated behind 

 the posterior wall of the tympanum ; within it are numerous 

 openings; five of these belong to the three semicircular 

 canals, and a larger one, in front of the others, leads to the 

 cochlea. A vertical ridge, called the crista, traverses the 

 inner wall ; below this is a small circular depression, the 

 fovea hemispherica, perforated by minute orifices which 

 transmit nervous filaments ; this depression corresponds to 

 the bottom of the meatus auditorius internus. On the roof 

 of the vestibule is another oval depression called the fovea 

 semi-elliptica. Behind the crista, and near the common 

 opening of two of the semicircular canals, is the internal 

 opening of the aquseductus vestibuli, the other orifice of 

 which is on the posterior surface of the petrous portion of 

 the temporal bone; through it pass a small artery and vein. 

 9 



