AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BT THE BIBLIOGRAPHIC SERVICE, JANUARY 19 



THE MORPHOLOGY OF THE SOUXD-TRANSIVIITTING 



APPARATUS IN CAUDATE AAIPHIBIA AND 



ITS PHYLOGENETIC SIGNIFICANCE 



H. D. REED 



Zoological Laboratory, Cornell University 



EIGHTEEN TEXT FIGURES AND SIX PLATES 



INTRODUCTION 



In earlier papers Kingsbury and Reed ('08 and '09) pointed out 

 the existence of two structures composing the sound-transmitting 

 apparatus of the tailed amphibians. One of these structures they 

 called columella which is extraotic in origin and is connected, 

 either directly or by a ligament, with the suspensorium of the 

 lower jaw. In the typical state it functions as the organ of sound 

 (jar) transmission during larval life. This condition is probably 

 the one which prevailed in primitive Caudata. The other ele- 

 ment was designated operculum which functions during adult 

 (terrestrial) life. It makes its appearance at the period of trans- 

 formation in such forms as Amblj^stoma and, upon completion, 

 becomes connected with the suprascapula through the AI. 

 opercularis. The operculum arises as a circular plate of cartilage 

 'cut out' from the walls of the ear capsule caudad of the primary 

 fenestra which is occupied by the columella and is, therefore, 

 otic in origin. The secondary fenestra which it occupies is 

 formed at the same time and by the same method as the element 

 itself. As the operculum completes the formative period and 

 assumes a functional role, the columella gradually fuses with the 

 cephalic margin of the fenestra and probably ceases to function, at 

 least, to any extent. 



In these papers the authors discussed the various morphological 

 relations of the columella and operculum and pointed out the 

 evidence which seemed to favor the hyomandibular homology' of 



325 



JOURNAL OF MORPHOLOGT, VOL. 33, NO. 2 



