TBE AUDITORY AITARATUS. 955 



passes over the stapes, after being reflected around the margin of the fenestra 

 ovalis. 



(These bones transniit ilje vibrations of the membrana tjmpani to the fluid 

 in the labyrinth.) 



5. Ligaments of the Auditory Bones. — "We need only mention the 

 existence of these here, as they are too small and unimportant to merit a 

 particular descri{)tion. 



0. Muscles of the Auditory Bones, — Four muscles have been described : 

 three for the malleus, and one for the stapes. But two of these being extremely 

 small, and their muscular character doubtful to many anatomists, we will only 

 notice the infernal muscle of the imdieus and that of the stapes. 



a. The internal musde of the malleus {tensor tijmpani, musrulus inte)-nus 

 mallei). — This is a little elongated fasciculus, lodged in a particular groove in 

 the mastoid portion of the temporal bone. It arises near the superior extremity 

 of the Eusta(;hian tube, and passes downwards and backwards, to terminate by 

 a tendon which is reflected outwards, in front of the fenestra ovalis, and is 

 inserted into the neck of the malleus. 



b. Muscle of the stapes {stapedius). — Lodged in an excavation in the inner 

 wall of the tympanum, near the fenestra vestibuli, on the course of the aquteductus 

 Fallopii, this muscle is remarkable for its brevity, its relatively considerable 

 thickness, and its conical shape. It terminates by a small tendon in front of the 

 head of the stapes. In the Horse, Ox, and Sheep, a small bony nucleus is found 

 in the tendon (Fig. 510, o). 



(The tensor tympani retracts the bones of the ear inwards. In contracting 

 it draws the handle of the malleus towards the cavity of the tympanum, and 

 this brings the membrane with it ; consequently, the convexity of 'the latter is 

 increased and its tension is augmented. In addition, while the handle of the 

 malleus is carried inwards, its head is turned outwards by a pivoting motion, and 

 this pulls the body of the incus also, the long process of which is raised and 

 inclined inwards, pushing the os orbieulare and stapes towards the fenestra 

 ovalis. The base of the latter bone being in contact with the fluid m the 

 vestibule, this is stirred ; so that this muscle likewise acts indirectly in producing 

 the undulations in this fluid. The muscles of the tympanum are classed as 

 tensors and laxators. It is well to know that all are tensoi-s, and none of them 

 act as relaxors ; relaxation of the membrane occurring when the muscles are not 

 in action.) 



5. The Mucous Membrane of the Tympanum. 



Very line and vascular, this membrane covers all the angularities of the 

 middle ear, is reflected on the chain of bones, and is continued into the mastoid 

 cells. It is continuous with that lining the Eustachian tube, and therefore 

 should be considered as a prolongation of the tegumentary membrane spread 

 over the walls of the pharyngeal vestibule. It is covered by a simple pavement 

 epithelium. 



6. The Eustachian Tube. 



The Eustarhian tube is a fibro-cartilaginous canal between the cavity of the 

 middle ear and the pharynx. 



Extending in a straight line beneath the base of the cranium, from the 

 tympanic case to the upper and lateral part of the pharyngeal cavity, this canal 



