MIDDLE EAR. 369 



os-orbiculare. It consists of a head, neck, base, and two 

 crura. Its head is hollow for receiving the os-orbiculare. 

 The neck gives attachment to the stapedius muscle. The 

 base is a flat, oval-shaped plate, like the foot of the stirrup, 

 and is attached to the membrana vestibuli. The two crura 

 or branches extend between the neck and base. 



These little bones are connected together by regular 

 articulations, having synovial membranes, and capsular 

 ligaments ; with an additional security of three other liga- 

 ments one going from the head of the malleus, to the 

 superior wall of the tympanum ; a second connecting the 

 short process of the incus with the mastoid cells ; the third, 

 a circular ligament, surrounding the margin of the fenestra 

 ovalis, and connecting it with the base of the stapes. 



Muscles of the Tympanum. Anatomists are not agreed 

 as to the number of these muscles some making four, 

 others three, and others two; the discrepancy arising from 

 one or two of these muscles being considered as ligaments. 

 The membrana tympani has two muscles a tensor and a 

 laxator. 



Tensor Tympani (or internal muscle of the malleus) 

 arises from the Eustachian tube, the spinous process of the 

 sphenoid bone, and from the petrous portion of the tempo- 

 ral. It has distinct fleshy fibres, which are lodged in the 

 canal above the Eustachian tube, and entering the tympa- 

 num at its forepart, are inserted into the handle of the mal- 

 leus below the processus-gracilis. Function. To draw the 

 handle inward, and thus make tense the membrana tympani. 



Laxator Tympani (or external muscle of the malleus) 

 arises from the spinous process of the sphenoid bone goes 

 through the glenoid fissure, and is inserted into the pro- 

 cessus gracilis. Function. To relax the membrana tym- 

 pani. This muscle is often found to be only a ligament. 



Laxator Tympani Minor is also regarded as simply a 

 ligament of fibrous cord, extending from the handle of the 

 malleus, below the short process, to the upper margin of 

 the rneatus. 



Stapedius. This little muscle, which has been also 

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