In the human instrument all the organs act together as a unit; so the fact that the cavities alone may affect the pitch is practically of no great significance.
THE TONGUE The tongue and the lips are the articulating organs, and the former has an important part to play in altering through its movements the shape of the mouth cavity.
The tip of the tongue should habitually rest against the under front teeth.

The tip of the tongue, however, must frequently touch the roof of the mouth near the upper front teeth, as when pronouncing the consonants _c_, _d_, _g_ or _j_, _l_, _n_, _s_, and _t_.

The back part of the tongue must rise a little to close against the soft palate when pronouncing _g_ hard, and _k_, and hard _c_, _q_, and _x_.

The soft palate comes down so far to meet the tongue that the elevation of the latter need be but very slight.
When speaking, the demand is not so imperative, but when singing, the body of the tongue should lie as flat as possible, so as to enlarge the mouth, especially when giving the vowel sounds.
If the tongue is sometimes disposed to be unruly, it is the result of rigidity or misplaced effort in the surrounding parts.

This tendency will only be aggravated by artificial restraint of any kind.