198 JAY ARTHUR MYERS 



opened and one of the sterno-tracheal muscles was dhnded at .4 

 (fig. 2). After this operation the tones produced by the chicken 

 were of a somewhat different quality. When both muscles were 

 cut the quaUtj^ of voice was even more distinctly modified. Ob- 

 viously the di^dsion of these muscles was responsible for the 

 changes produced. Some weeks later this same chicken was 

 anaesthetized and electrodes applied both directly to the sterno- 

 tracheales and to the nerves supplying them. It was observed, 

 udth some surprise, that the division of these muscles apparently 

 had but little effect upon the actual shortening of the trachea. 

 On stimulation the muscles immediately contracted and pro- 

 duced a marked shortening. By way of explanation, it should 

 be recalled that the tjmipanum is attached to the pessulus and 

 the first intermediate syringeal cartilages only by elastic mem- 

 branes; that, although the ventral ends of the intermediate car- 

 tilages are attached to the ventral pyramid of the pessulus, the 

 dorsal ends of these cartilages are unattached, and that all of 

 these cartilages are connected with each other by the intercarti- 

 laginous membranes. Further, the external tympanic mem- 

 branes are attached to the caudal borders of the fourth intermedi- 

 ate cartilages. Now, if the tympanum be drawn cephalad it is 

 evident that the external tympanic membranes will, indirectly, 

 be made more tense. Under normal conditions stimulation of the 

 sterno-tracheales serves to shorten the trachea. They tend to 

 pull the caudal end of the trachea cephalad; especially is this the 

 case if there be a simultaneous contraction of the dorso-lateral 

 and ventro-lateral muscular bmidles pre\dously described. The 

 extent of this shortening of the trachea is prevented, however, 

 to some extent by the sternal attachments of the sterno-tracheales. 

 Hence, when these attachments are severed, the contraction of 

 the tracheal parts of these muscles tend to make the external 

 tympanic membranes more tense and a modification in the qual- 

 ity of the voice is the result. It is of course probable that other 

 factors, more physical than the above, also share in the produc- 

 tion of the modification observed. 



From their structure it is evident that the external and the 

 internal tympanic membranes are vibrating structures. As in 



