The tongue is a veritable stumbling block in the path of the singer. The tongue is an enormous muscle compared with the other parts of the throat and mouth, and its roots particularly can by a slight movement block the passage of the throat pressing against the larynx. This accounts for much of the pinched singing we hear.
When the tongue forms a mountain in the back part of the mouth the singer produces what you call in English slang "a hot potato tone"—that is to say, a tone that sounds as if it were having much difficulty to get through the mouth. In very fact, it is having this difficulty, for it has to pass over the back of the tongue.
The would-be singer has to learn to control the tongue muscles and, above all things, to learn to relax the tongue and to govern it at will, so that it never stiffens and forms that hard lump which can be plainly felt immediately beneath the chin under the jaw.
It requires a great deal of practice to gain control of the tongue, and there are many different exercises which purport to be beneficial in gaining complete mastery over it. One, for instance, is to throw the tongue out as far forward as possible without stiffening it and then draw it back slowly. This can be done in front of a mirror by trying to throw the tongue not only from the tip, but from the root, keeping the sides of the tongue broad. Another way is to catch hold of the two sides of the tongue with the fingers and pull it out gently.
For my part, I scarcely approve of these mechanical ways of gaining control of the tongue except in cases where the singer is phlegmatic of temperament and cannot be made to feel the various sensations of stiff tongue or tongue drawn far back in other ways. Ordinarily I think they make the singer conscious, nervous and more likely to stiffen the tongue in a wild desire to relax it and keep it flat.
These exercises, however, combined with exercises in diction, help to make the tongue elastic, and the more elastic and quick this muscle becomes the clearer will be the singer's diction and the more flexible will be her voice.
The correct position of the tongue is raised from the back, lying flat in the mouth, the flattened tip beneath the front teeth, with the sides slightly raised so as to form a slight furrow in it. When the tongue is lying too low a lump under the chin beneath the jaw will form in singing and the tight muscles can be easily felt.
When the jaw is perfectly relaxed and the tongue lies flat in the mouth there will be a slight hollow under the chin and no stiffness in the muscles.
The tip of the tongue of course is employed in the pronunciation of the consonants and must be so agile that the minute it has finished its work it at once resumes the correct position.
In ascending the scale the furrow in the tongue increases as we come to the higher notes. It is here that the back of the palate begins to draw up in order to add to the resonance of the head notes, giving the cavities of the head free play.