MIDDLE-EAR REGION OF GALLUS 235 



birds, and attention was then called to the position of certain 

 elastic ligaments which are practically constant in all birds 

 examined. More detailed investigation has been undertaken 

 to ascertain the functional relation of these elastic ligaments to 

 the action of the M. tensor tympani, to the drum membrane, 

 and to the columellar apparatus. Breuer has undoubtedly 

 described the muscle correctly as one without an opponent, and 

 the structure should be of interest to the physiologist in deter- 

 mining the possibility of a dual nerve supply; an excitor-inhibitor 

 system as found in involuntary muscles or in the voluntary 

 muscles with opponents as proposed in Sherrington's reciprocal 

 innervation. 



The scope of this paper, based almost entirely on Gallus, will 

 be limited, first, to the description of the elastic elements of this 

 region and to the mechanical features in the columellar system; 

 second, to an interpretation of the mechanism of the bird's 

 middle ear. 



The material used consists of newborn and semiadult chickens, 

 fixed in Bouin's fluid or in formalin, decalcified in hydrochloric 

 acid-alcohol and sectioned in collodion or paraffin. The sec- 

 tions were stained in Weigert's resorcin-fuchsin or in orcein, 

 and for the most part differentiated in acid alcohol. The col- 

 lodion sections were all cut at 50ju, the paraffin sections at 25;u. 



ELASTIC TISSUE OF THE EXTERNAL AUDITORY CANAL 



The external auditory canal in the chicken leads obliquely 

 downward and backward from its oval external opening which 

 is protected by the upward projection of the lower bordering 

 feathers. The orifice lies well in front of the short bony external 

 canal and is situated in a plane at right angles to the position of 

 the drum membrane. The canal has a distinct kink in it and 

 particularly the ventral-median wall is bent upon itself so that 

 the most external part is applied to the side of the head. The 

 dorsal wall of the canal is longer than the ventral, because of the 

 oblique position of the drum membrane, and is reinforced by a 

 heavy fibrous plate which is attached to the edges of the bones 

 surrounding the region, with the exception of the quadratum. 



