The vibration of the vocal fold was X-ray stroboscopically analysed in canine larynx. The vibration was observed mainly from the frontal plane view. In addition, simultaneous cinematography was carried out from the ordinary direction by a laryngeal stroboscope.
An overall image, and the trajectory movements of the tiny lead particles injected into the various parts of the fold were observed and analysed. These studies were performed while the pitch and intensity of the experimental phonation were changed.
If the vibration is supposed to be composed of each movement of every part of the fold which has differential phase and amplitude to each other, it seems most likely that the essential principle of the vibration is a travelling wave which moves to lateral upward from the lower surface of the fold.
The size of the trajectory of the point at the so-called free edge is the largest and almost circular. Both of the vertical and horizontal components of this movement move faster than the movements of the other parts of the fold.
With higher pitch, the movement of the point is decreased in size and the vibratory part of the fold is narrowed.
On the other hand, with higher intensity, the movement of the point is remarkably increased and the vibratory part is extended.
However, the essential of the principle of the vibration is persistently a travelling wave itself in any condition.

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