This position of the lips also gives freedom for pronunciation.

"The upper lip plays the most active part in the shaping of the vowels.

It should never be drawn against the teeth when producing vowel tones; indeed, there should be often a little space between the upper lip and the teeth, so that the vibrations of the sound-waves can have free play." THE NOSTRILS The nostrils should be dilated as much as possible, as a free, wide, open nose gives a free, well-rounded tone, while a contracted nostril induces the nasal tone so much dreaded.

A proper training of the facial muscles makes this dilation possible.

Lifting the upper lip and projecting it forward aids the action to a great degree.
There is a strong tendency to unity of action between the nostrils and the lips and the soft palate.