The author was himself unable fully to appreciate this until he had become able to sense the position of the soft palate during vocalization.
THE HARD PALATE AND TEETH The hard palate and upper teeth form in part the walls of the mouth.
As they are solid fixtures, nothing can be done in the way of training.

They furnish a point of impingement in articulation, and play their part in sympathetic resonance.
The bones which form the roof of the mouth serve also for the floor of the nasal cavity.
The under teeth also serve as walls of resistance to support the tongue during the performance of its functions.
THE NASAL AND HEAD CAVITIES The nasal and head cavities are resonating chambers incapable of special training, but their form, size, and the use made of them have a wonderful effect upon the resonance of the voice.

If the vibrations are strong here, all other parts will vibrate in harmonious action.
When responding to the perfectly focused tone the thin walls of the cavities and the contained air vibrate with surprising force, often for the moment blinding the singer when sounding a note intensely.
Having in my surgical work demonstrated the existence of a hitherto unrecognized connecting passage or canal between the air cavities of the face and those of the forehead,[2] the play of resonance in the cavities above the nostrils is more easily understood.

The function of the cavities known as the _frontal sinuses_ (see Fig.

1) has long been a mystery, but now that their direct connection with the lower cavities is proven, and the great significance of resonance is also beginning to be recognized, the mystery disappears.