THE STAPEDIUS. 1157 



the membrane tense will be much less than its actual power, while, on 

 the other hand, the amplitude of movement at the point of resistance 

 will be considerable. 



Again, when the muscle is in a state of contraction, it renders all the 

 ligaments of the ossicles tense, with the exception of the superior 

 ligament of the malleus. This effect may be seen in the human 

 subject, if the tympanum be opened during rigor mortis. 



The normal stimulus which causes the tensor tympani to contract 

 is the pressure of sound-waves on the membrana tympani. Although 

 the innervation of the membrana has not been conclusively established, 

 there is little doubt it is supplied with sensory nerves by the fifth, and 

 also by the tympanic plexus, formed by fibres derived from the otic 

 ganglion, from the petrosal ganglion of the glosso-pharyngeal, and from 

 the carotid plexus. 1 When pressure is made on the membrana, there 

 is irritation of these sensory nerves, followed by a reflex contraction 

 of the tensor tympani, supplied by a motor filament from the motor 

 division of the fifth nerve. 2 This response to sound was first discovered 

 by Hensen and Bockendahl. 3 They attached a light signal to the 

 tendon of the muscle in the dog, and observed a movement when a 

 note was sounded. Pollak 4 found that when one ear was stimulated 

 by sound-waves, the tensor tympani on the opposite side was also 

 thrown into contraction. He also found that the reflex contraction 

 was most marked when a tone of high pitch was sounded, deep tones 

 causing only very slight contractions. The tensor tympani also con- 

 tracts during yawning. In a few rare cases, the muscle appears to be 

 under control of the will. 5 



The stapedius. Henle 6 was of opinion that the stapedius, when 

 it contracted, held the plate of the stapes firmly in its place, and 

 prevented it being forced into the fenestra ovalis, when strong pressures 

 were communicated to it from the membrana tympani. On the other 

 hand, Politzer 7 endeavoured to demonstrate that contraction of the 

 muscle draws the plate of the stapes out of the fenestra ovalis, and, 

 by releasing the tension of the chain of bones, produces relaxation of 

 the membrana tympani. According to this view, the stapedius is the 

 antagonist of the tensor tympani. The stapedius is supplied by a 

 branch of the facial nerve. We have no direct evidence of any reflex 

 excitation of the stapedius, but one would expect it to respond in a 

 manner analogous to the response of the tensor tympani. Lucae 8 

 suggests that it may respond to tones of high pitch, and he also 

 mentions that contraction of certain muscles of the face, especially 

 of the orbicularis palpebrarum, causes a simultaneous contraction of 

 the stapedius. 



The movements of the ossicles as a whole under the influence 

 of sound-waves. When a sound-wave strikes the membrana tym- 

 pani, that structure will be driven inwards during the positive phase ; 

 that is to say, during the time when the pressure is greater than 



1 Bischoff, " Mikroskopische Analyse der Kopfnerven, " Munich, 1865. 



2 Politzer, Jahresb. il. d. Leistung . . . in d. Anat. u. PhysioL, Berlin, 1860, S. 583 ; 

 and Voltolini, Virchow's Archiv, Bd. Ixv. S. 467. 



3 Arch.f. Ohrenh., Bd. xvi. S. 253. 4 Med. Jahrb., Wien, 1886. 



5 Schwartze, Arch.f. Ohrenh., Bd. ii. ; Lucae, ibid., Bd. iii. ; and others. 



6 "Handbuch d. Anat. des Menschen," Bd. ii. "Eingeweidelehre," S. 749. 



7 Wien. med. Wchnschr., Bd. xvii. S. 1657 ; Bd. xviii. S. 113. 



8 Politzer, " Diseases of the Ear," 1894, p. 69. 



