MIDDLE-EAR REGION OF GALLUS 233 



bj' introducing- a protected electrode into the foramen communicans 

 just posterior to posterior canal. Here the electrode is in contact with 

 the N. facialis and the other electrode may be placed on an indifferent 

 part of the bird's body. When the circuit is closed, the head of the 

 columella is drawn backward and downward; the upper and anterior 

 quadrants of the drum are rendered tense and the concavity of the 

 conical surface is decreased. The lower quadrant is rendered more 

 tense from before backward but because the head of the columella 

 slips downward, it is relaxed in this direction. (This makes it simple 

 to understand why Breschet called the muscle a laxator memb. tym- 

 pani because one would assume, unless it was demonstrated to him, 

 that a M. tensor tympani would not under any circumstances be an 

 extrinsic muscle of the middle ear.) 



The columella returns to its original position when the stimulation 

 of the N. facialis ceases. This comes about through the elasticity of 

 the cartilaginous processes which were bent through muscular contrac- 

 tion. Particularly the lower process, which Breschet homologizes with 

 the proc. gracil. mallei, seems to react because of its spring-hke f orm ; 

 while the upper cartilage process seems to prevent too great a back- 

 ward displacement by pressing against the drum border. When the 

 head of the columella is pulletl backward, the plate closing the oval 

 window must also be influenced. In what manner is this accomplished 

 and how is the cochlea affected by this displacement? 



In the experiments on the stimulation of the N. facialis in the pigeon, 

 the cochlear area was necessarily thorough^ exposed. Fine droplets 

 of perilymph appeared on the surface through the small crevices in the 

 bone occasioned by the dissection. These tiny holes were also inten- 

 tionally produced by boring into the bony wall of the cochlea with a 

 needle, and with the same result. When the N. facialis trunk was 

 stimulated the small drops of perilymph were immediately sucked into 

 the cochlea and would reappear as soon as the stimulation ceased. 

 The contraction of the M. tensor tympani therefore tends to reduce the 

 pressure within the perilymphatic space. 



If one opens the cochlea from its cranial aspect and removes the 

 membranous labyrinth, one may readily observe the columellar foot- 

 plate. If the tendon of the M. tensor tympani is pulled on, one may 

 see that the proximal anterior border of the columellar plate appears 

 to be displaced. I have used the word 'appears' because the traction 

 upon the tendon of the muscle in the manner described is, after all, a 

 rough experiment but the displacement is quite probable from the 

 anatomical relation of the parts themselves. 



It does not appear possible to homologize this muscle with the intrin- 

 sic ear muscles of the mammals. A comparison with the M. retractor 

 auriculae is more readily accomplished. A functional comparison is 

 however readily made. It seems certain that a muscle which attaches 

 to the head of the columella; draws it backwards; displaces the sta- 

 pedial plate out of the fenestra vestibuh; and reduces the pressure 

 within the labyrinth — is a complete functional analogue of the mam- 



