250 A. G. POHLMAN 



operculum is fixed in place, partly by a hinge in the cartilage 

 and also by a stout elastic hgament which appears to have a 

 functional relation to the M. opercularis as determined by 

 Ahearn in an unpublished thesis on the anuran ear. 



MECHANICS OF THE COLUMELLA AND EXTRACOLTOIELLA 



The results of the contraction of the M. tensor tympani are 

 apparently in accord with Breuer's statement — downward, 

 backward, outward displacement of the extrastapedial and an 

 increase in tension of the anterior-superior drum quadrants. 

 The changes in the drum membrane can naturally only come 

 about through displacement of the extracolumella. The mechan- 

 ics of this displacement and its effect upon the columella demand 

 a more detailed description. The writer does not feel that drum 

 tension itself has any very important relation to the problem, 

 but rather that it is a result of adjustment of drum position. 



Close inspection of the columellar apparatus in situ reveals 

 four distinct kinds of movement. The first of these is a more 

 or less typical plunger motion of the columellar foot-plate in 

 and out of the fenestra vestibuli. The other three are hinge-like 

 in character and are dependent either on the displacement of the 

 extracolumella as a whole or upon bendings which take place 

 in the extracolumella itself. These three movements will be 

 described under the terms columellar hinge, suprastapedial 

 hinge, and extrastapedial hinge. It must of course be remem- 

 bered that the hinges in the cartilage are much of the same char- 

 acter as the operculmn hinge in amphibians — merely weakened 

 areas which permit a bending and not true joints. 



The movement of the columellar foot-plate in the fenestra 

 vestibuli is more or less an in-and-out motion probably combined 

 with a slight tilting as found in the mammalian stapes. Unlike 

 the condition in the mammal, however, where the force is 

 directly applied to the bony stapes, the movement is imparted 

 to the columellar foot-plate through the bony columellar lever 

 by a tilting of the elastic extracolumella. The result of this is a 

 final direct push and pull of the relatively long bony columella 

 upon its foot-plate, or a resultant limitation of the tilting which 



