676 



DISSECTION OF THE EAR. 



Fig. 242. 



to the bone supporting it. And the base of the stapes is connected to the 

 margin of the fenestra ovalis by fibres constituting an orbicular ligament. 

 In the recent bone the thin mucous membrane closes the interval be- 

 tween the crura of the stapes, and is attached to the groove on the inner 

 aspect. 



Muscles of the ossicles (fig. 242). Three muscles which possess trans- 

 versely striated fibres are connected with the chain of bones ; two of these 

 are attached to the malleus, the other to the stapes. 



The tensor tympani (fig. 242, h) (internal muscle of the malleus) is the 

 largest and must distinct of the muscles of the tympanum, and takes the 

 shape of its containing tube, which must be laid open to see it completely. 

 The muscle arises from the surface of its bony canal, also slightly in front 

 from the cartilage of the Eustachian tube. Posteriorly it ends in a ten- 

 don which is reflected over the end of the 

 cochleariform process, and is inserted in- 

 to the inner border of the handle of the 

 malleus, near its base. 



Action. The muscle draws inwards 

 the handle of the malleus towards the in- 

 ner wall of the tympanic cavity, and 

 tightens the membrane of the tympanum ; 

 and as the long process of the incus is 

 moved inwards with the malleus the base 

 of the stapes will be pressed into the 

 fenestra ovalis. 



Laxator tympani (fig. 242, g] (exter- 

 nal muscle of the malleus). It is con- 

 nected externally with the spinous process 

 of the sphenoid bone ; and passing through 

 the Glaserian fissure, it is attached to the 

 neck of the malleus above the processus 

 gracilis. 



Action. The muscle draws inwards and 

 forwards the upper part of the malleus, 

 and tilts outwards the handle, so as to re- 

 lax the membrana tympani ; and on the 

 cessation of the contraction of the tensor, 

 it can move out the bony chain. 



The stapedius (fig. 242, ?') is lodged 

 in the canal holowed in the interior of 

 the pyramid. Arising inside the tube, 

 the muscle ends in a small tendon, which 

 issues from the pyramid, and is inserted 

 into the neck of the stapes at the poste- 

 rior part. 



Action. By directing the neck of the 



stapes backwards the muscle raises the fore part of the base out of the 

 fenestra ovalis, diminishing the pressure on the fluid in the vestibule ; and 

 supposing it to contract simultaneously with the tensor, it would prevent 

 the sudden jar of the stapes on that fluid. 



Mucous membrane of the tympanum. The mucous lining of the tym- 

 panic cavity adheres closely to the wall ; it is continuous with that of the 



PLAN OP THE OSSICLES IN POSITION IN 

 THE TYMPANUM WITH THEIR MUS- 

 CLES. 



a. Cavity of the tympanum. 



fe. Membrana tympani. 



c. Eustachian tube. 



d. Malleus. 



e. Incus. 

 /. Stapes. 



g. Laxator tympani muscle. 

 h. Tensor tympani. 

 ?. Stapedius. 



