At present the leading authorities recognize three registers, chest, medium, and head, corresponding to the lower, middle, and higher parts of the range of the voice. Individual voices vary in their possession of registers. Tenors usually have only the medium and head, the falsetto (confined generally to this voice) being in most cases of too effeminate a quality for use in artistic singing. Baritones usually have all three registers, basses only chest and medium. Sopranos may possess all three, although the chest register is seldom well developed in this voice. Mezzos have the chest and medium, and in the majority of cases the head register also. Contraltos possess the chest and medium, but very rarely the head register. Teachers have in most cases discarded the plan of giving precise limits to the registers and training them separately. It is considered the best practice to bring about the correct action of the medium part of the voice, including command of the crescendo and diminuendo on the single tone, before beginning to develop the higher and lower portions of the range. The compass is then gradually extended upward and downward, care being taken to avoid the breaks which almost always resulted from the older system of training the registers separately. Assistance is found in developing the low notes by the cultivation of chest resonance. High notes are helped by the use of nasal resonance and also by practice in attacking tones with the liquid or sonant consonants. Both these topics will be considered later. Three resonance cavities have to be brought under control, each of which acts independently of the others. These are the chest, the mouth-pharynx, and the nasal cavities. As a rule the influence of chest resonance is most marked in the lower part of the voice. The mouth-pharynx (in addition to its almost exclusive province of vowel and consonant formation) reinforces the entire range, and the nasal cavities contribute most to the high notes. It must not be understood, however, that in artistic singing chest resonance is to be used only on low notes and nasal resonance on high notes. The special function of nasal resonance is believed to be the imparting of brilliancy, point, and carrying power to the tones. While its effect is more marked on the high notes, it must always be present in some degree throughout the entire compass of the voice. Breadth and sonority of tone are supposed to be contributed by chest resonance, and these must also be present on all loud tones, whether high, medium, or low.