The air passages above the larynx are known as the vocal tract. This is usually considered to be divided into two cavities:
- nasal cavity
- oral cavity
The pharynx is the cavity that leads from the back of the mouth and the nasal passages to the larynx and esophagus (which leads to the stomach). It is shaped somewhat like an inverted cone and may be considered as a tube of muscle that is approximately 12 cm long. Strictly, the oral cavity extends from behind the teeth to the pharynx. Sometimes a third cavity, the buccal cavity, is identified. This extends from behind the lips and cheeks to the front surfaces of the teeth. However, for most purposes it is sufficient to consider the oral cavity as the area occupying the space between the lips and the pharynx.
The lower surface of the nasal cavity is the upper surface of the oral cavity and we have seen that this consists of the palate. The front portion of the palate is a bony structure, known as the hard palate. The hard palate ends almost level with the back molar teeth. The remaining rear portion is a flexible muscular flap, known as the soft palate or velum. At the end of the soft palate there is a small appendage that hangs down. This is known as the uvula. It is the piece of soft, fleshy tissue that can be seen hanging down at the back of the mouth whilst someone continually vocalizes the vowel ‘ah’ as in the words car, father and hark. The soft palate can be raised so as to close the nasal cavity and prevent air escaping through the nose.
Figure 1. Vocal Tract (click for an enlarged image)
In addition to these upper surface features of the hard palate, there is a bony protuberance just behind the upper incisors. This is known as the alveolar ridge (gum ridge).
On the floor of the oral cavity is the tongue. The tongue is a large muscular organ covered by a mucous membrane that keeps it moist and lubricated. It is an extremely strong and flexible muscle. The whole upper surface of the tongue, the underside of the front portion, and the sides are all unattached and, therefore, free to move. The remainder of the tongue is attached at various places within the oral cavity. Because the oral cavity contains moving parts the relative size and geometry of the cavity can be altered, e.g. the tongue can take up different positions, the lips can be protruded or spread, the jaw can be opened or closed.