Tensions in the tongue and jaw are all too common for singers. What a nuisance they can be! I once read that even Dame Kiri Te Kanawa had problems with her tongue in the beginning. It always seemed to get in the way! That´s really comforting, though, isn´t it for the rest of us!
Why would one be too tense in these important parts of our instrument? We need them all the time, for eating and drinking mostly, for speaking and singing always too. The jaw muscles are very strong indeed and have gained strength through daily practice. Our nervous system is connected to all muscles and we may keep the jaw muscles tight even while sleeping. Sometimes we even clench our teeth, whether awake, nervous or angry, or during the night , our subconscious stress manifesting itself in the tightness of the masseter and pterygoid muscles (biting muscles).
Try to sing with your teeth together. The space in the pharynx obviously diminishes but the muscles connected to the hyoid bone and all the way to the larynx are also affected. That is why we should relax the jaw when singing. The opening of the mouth aperture is actually not the most important thing, but the loose feeling between the jaws, some space between the molars, is actually very important. In our speech we are sometimes accustomed to pronouncing some vowels with a spread mouth opening, for ex. Italian i (ee) or e (eh). In singing this opening may be too tight and it may also be difficult to open the jaw for higher pitches.
How to open the mouth correctly?  Funny, but this can really be an issue especially for beginning singers. Find the spot where the jaw can be unhinged, situated in front of the ears. Let the jaw move slightly forward, then down and back, not directly backwards and down. You don´t need a constantly hanging jaw like an idiot, but you must be able to open to maximum at will on certain higher pitches. If the opening is not correct it may hinder the ease of high notes and cause tensions elsewhere. This movement should be automatic and coordinated according to the range of a sung phrase; singing should never be “led” by the jaw.
The other culprit, the tongue, is really an artist! It helps in molding the cavities into different vowel formants and moves like a quick little snake to all possible syllable forms. Really a surprisingly multitasking organ, it also likes to “help” when there is a balance problem. The root of the tongue can unfortunately do much harm to the beauty of the sound, make a wide range difficult and create problems for the pronouncing of words. (See my previous article). Sometimes we hear a sound that has been dubbed “Knödel”, a German word meaning there´s a hot potato in your throat. That sound is instinctively produced by children mockingly imitating opera singers! But no so! It´s too bad a singer cannot really hear it himself. In the singer´s ears the sound may just be darker and more “professional”, whereas in reality it sounds muffled and hollow. So we should get rid of that tension as soon as possible. But how?
It can be very difficult to correct, I must say. And yet, with lots of practicing and a good pair of other ears it is possible. First and foremost, don´t try to listen to yourself too much (it´s inevitable of course) but go for the good feeling in the throat and  tongue root. Check your body connection and support for too much pressure. Remember support is about elasticity, not rigid force. Check your head position and the back of your neck (also important for the jaw). For exercise, try rolling your tongue out as far it can go, feeling a good stretch way back in the throat. For singing, find a tongue position very forward in the mouth and keep this as your “home base” to which the tongue always returns after its adventures inside the mouth for different consonants. Relax the tongue with every inhalation, returning to this position. Avoid pressing to tongue against the front teeth but do keep it slightly in touch with your lower front teeth. It is possible to pronounce all vowels in this position but if you are used to something else it may be strange at first.
I´m quite aware there are lots of great singers whom we see singing with their tongues tipped up against the palate or in any other positions.  We are all individuals and they possibly have such big cavities that tiny adjustments just don´t count. But most singers less endowed might find these tips helpful I hope.