454 MUSCLES OF THE TYMPANUM. 



The Muscles of the tympanum are four in number, the 



Tensor tympani, 

 Laxator tympani, 

 Laxator tympani minor, 

 Stapedius. 



The Tensor tympani (musculus internus mallei) arises from the 

 spinous process of the sphenoid, from the petrous portion of the 

 temporal bone, and from the Eustachian tube, and passes forwards 

 in a distinct canal, separated from the tube by the processus coch- 

 leariformis, to be inserted into the handle of the malleus, imme- 

 diately below the commencement of the processus gracilis. 



The Laxator tympani (musculus externus mallei) arises from the 

 spinous process of the sphenoid bone, and passes through an opening 

 in the fissura Glaseri, to be inserted into the long process of the 

 malleus. 



The Laxator tympani minor arises from the upper margin of the 

 meatus, and is inserted into the handle of the malleus, near to the 

 processus brevis. This is regarded as a ligament, by some anato- 

 mists. 



The Stapedius arises from the interior of the pyramid, and escapes 

 from its summit to be inserted into the neck of the stapes. 



The openings in the tympanum are ten in number, five large and 

 five small; they are 



Large Openings. Small Openings. 



Meatus auditorius, Entrance of the chorda tympani, 



Fenestra ovalis, Exit of the chorda tympani, 



Fenestra rotunda, For the laxator tympani, 



Mastoid cells, For the tensor tympani, 



Eustachian tube. For the Stapedius. 



The opening of the meatus auditorius has been previously de- 

 scribed. 



The Fenestra ovalis (fenestra vestibuli), is a reniform opening, 

 situated at the bottom of a small oval fossa (the pelvis ovalis), in 

 the upper part of the inner wall of the tympanum, directly opposite 

 the meatus. The long diameter of the fenestra is directed horizon- 

 tally, and its convex borders upwards. It is the opening of com- 

 munication between the tympanum and the vestibule, and is closed 

 by the foot of the stapes and by the lining membranes of both 

 cavities, 



The Fenestra rotunda (fenestra cochlea?) is somewhat triangular 

 in its form, and situated in the inner wall of the tympanum, below 

 and rather posteriorly to the fenestra ovalis, from which it is sepa- 

 rated by a bony elevation, called the promontory. It serves to 

 establish a communication between the tympanum and the cochlea. 



