234 A. G. POHLMAN 



maliaii M. stapedius. But this muscle is, at the same time, one which 

 increases the tension of the drum membrane. Functions, which in 

 mammals, are divided between two antagonistic muscles, are therefore 

 accomplished in birds by a single muscle which not only renders the 

 drum more tense but also decreases the intra-labyrinthine pressure. 

 If both of these functions may be merged in the bird, the M. tensor 

 tympani and M. stapedius of the mammals cannot properly be classed 

 as muscles of opposition. 



Breuer's conclusions on the function of the M. tensor tympani 

 in birds are: 



That it combines the action of the mammalian M. tensor tympani 

 and M. stapedius in that it increases the drum tension and at the same 

 time decreases intra-labyrinthine pressure; second, because the single 

 muscle in birds replaces the double muscle in mammals, the two muscles 

 in the mammal cannot well be regarded as opponents but rather as 

 synergists; third, the M. tensor tympani possesses no muscle of opposi- 

 tion, and its contractions therefore have to do with preserving its tonus, 

 with maintaining the pliability of the columella and in particular, the 

 annular ligament attaching the columellar foot-plate to the margin of 

 the fenestra vestibuli; fourth, to compensate for minor mechanical 

 errors in the sound-transmitting apparatus (the nature of which he 

 does not suggest). 



Beyer ('07) describes the drum membrane in greater detail 

 and particularly in the matter of its attachments. An annulus 

 is not found in birds and the membrane is therefore attached to 

 the adjacent borders of the surrounding bones; the pars basilaris 

 of the sphenoid, the os occipitale laterale and basale, the squa- 

 mosum, and the tympanic process of the quadratum. The last- 

 named bone is movable, and may therefore influence the drum. 



STATEMENT OF THE PROBLEM 



Little \vork, apart from the notation in Bronn ('93), has been 

 done on the tuba auditiva. Here the common tubal orifice is 

 described as occupying a median position in the occipitosphe- 

 noidal suture. The right and left tubae fuse into a short com- 

 mon tube or duct which opens into the posterior part of the oral 

 cavity. 



It occurred to the writer ('14) that little work had been done 

 on the mechanical factors involved in the middle-ear region of 



