MUSCLES OF THE OSSICLES. 



811 



The TENSOR TYMPANI (fig. 299, h) is the larger of the two 

 muscles of the tympanum, and takes the shape of its containing 

 tube, which must be laid open to see it completely. The muscle 

 in front from the cartilage of the Eustachian tube and the 

 posterior extremity of the great wing of the sphenoid bone, and it 

 also receives fibres from the surface of its bony canal. Posteriorly 

 it ends in a tendon which is reflected over the end of the cochleari- 

 form process, and is inserted into 

 the inner border of the handle 

 of the malleus near its base. 



Action. The muscle draws in- 

 wards the handle of the malleus 

 towards the inner 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 ienestra 

 oval is. 



The STAPEDIUS (fig. 299, *) is 

 lodged in the canal hollowed 

 in the interior of the pyramid. 

 Arising inside the tube, the 

 muscle ends in a small tendon, 

 which issues at the apex of the 

 pyramid, and is inserted into the 

 back of the head of the stapes. 



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 sup- 

 posing it to contract simul- 

 taneously 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 tympanic cavity adheres closely to the wall ; it is continuous 

 with that of the pharynx through the Eustachian tube, and is 

 prolonged into the mastoid cells through the antrum. 



It forms part of the membrana tympani, and of the secondary 

 membrane in the fenestra rotunda ; it is reflected also over the 

 chain of bones, the muscles, ligaments, and chorda tympani nerve. 

 In the tympanum the membrane is thin, not very vascular, and 

 secretes a watery fluid ; but in the lower end of the Eustachian 

 tul>e it is thick and more vascular, and is provided with numerous 

 glands. 



Tensor 

 tympani : 



origin ; 



insertion ; 



Stapedius 



contained in 

 pyramid ; 



FIG. 299. PLAN OF THE OSSICLES OF 

 THE TYMPANUM IN POSITION, 



WITH THEIR MUSCLES. 



a. Cavity of the tympanum. 



Membrana tympani. 



Eustachian tube. 



Malleus. 



Incus. 



Stapes. 



Laxator tympani muscle, some- 

 times described. 

 h. Tensor tympani. 

 i. Stapedius. 



Lining of 

 tympaimm 



arrange- 

 ment in 

 cavity ; 



in Eusta- 

 chian tube. 



