In human anatomy, starting with the mouth is the first portion of the alimentary canal that helps in receiving food and produces saliva. The oral mucosa is represented by the mucous membrane and an epithelium lining is present in the inside of the mouth. Along with its primary role as the beginning of the digestive system, in humans the mouth also has a great significance in communication. Though the primary aspects of the voice are produced in the throat, the tongue, lips, and jaw are also equally needed to produce the different range of sounds included in speech. Mouth is also called the oral or the buccal cavity.

The mouth comprises two regions, the vestibule and the oral cavity. The mouth usually remains moist, as it is lined with a mucous membrane. It contains the teeth. The lips represent the transition from mucous membrane to skin, which also covers most of the body. In some of the invertebrate species that possess a hard exoskeleton, their mouth parts are also involved in feeding behaviour. Insects possess a diverse inner mouth anatomy that is well suited, according to their modes of feeding, in few cases consisting of mandibles – the lower jaw, maxillae – the upper jaw and labium – a fused mouth part that helps in  providing support for holding food in the mouth. These internal structures are modified in such a way that it forms suitable appendages for chewing, cutting, piercing, sponging and sucking. Surprisingly, in certain less advanced invertebrates like that of sea anemone, the mouth structure is designed in such a way that it facilitates in the expulsion of undigested food i.e. it functions as an anus also. 

Anatomy of Mouth 

The major structures of the mouth include:

• Lips: these are two in number, mobile and muscular structures that display the entrance to the mouth. The lips mark the transition from skin to moist mucous membrane.
• The Vestibule: it represents the space between the soft tissues (i.e. lips and cheeks), and the teeth and gums. The vestibule is usually kept moist by secretions from the parotid salivary glands, that are located in front of the ears and behind the angle of the jaw.
• Mouth cavity: the mouth cavity is mainly bounded by different structures. The alveolar arches (bony structures that contain the teeth) help in surrounding the mouth cavity from the front and on the sides – overhead are situated the hard and soft palates and below is the tongue. The secretions from the submaxillary and sublingual salivary glands help to keep the mouth cavity moist, these are located at the floor of the mouth beneath the tongue.
• Gums: are composed of the fibrous and dense tissue that covers the alveolar arches and surrounds the teeth.
• Teeth: a person possesses two sets of teeth during the course of their life. A child possesses their full set of minimum 20 primary (or milk) teeth by the age of three years. These primary teeth begin to fall out between the ages of six and seven years, and are simultaneously replaced by a permanent (or secondary or adult) set of teeth. Around 21 years, the average person possesses a maximum of 32 permanent sets of teeth; 16 in the upper jaw and 16 in the lower jaw.
• Palate: comprises both the hard and soft palates. The hard palate represents the bony roof of the mouth. Whereas, the soft palate is a fold of membrane that usually hangs between the mouth cavity and the back of the throat. The little hanging part that can be seen when the mouth is wide open is known as the uvula. 
• Tongue: it is almost entirely composed of muscle fibres. Tongue is  mainly divided into an oral portion (tip, blade, front, centre and back) and a pharyngeal (throat) region. The main function of the tongue is to taste, speak and swallow.
• Minor Salivary Gland: it represents a clear fluid by the name saliva and it keeps the mouth moist and contains enzymes that help in the breakdown of food. These glands are mainly located in various locations around the mouth, including the inner cheeks.

Trigeminal nerve

The trigeminal nerve is the main nerve of the face. Its functions include sensation along with some motor functions like that of biting, chewing and swallowing. It is also called as the fifth cranial nerve, it possess three main branches, including:

• Upper branch – provides the scalp and forehead.
• Middle branch – provides the cheeks, top lip, upper jaw, top teeth, gums and some areas of the nose.
• Lower branch – forms the bottom lip, bottom jaw, bottom teeth and gums.

Functions of Mouth

The primary function of the mouth is, the ingestion, and digestion of food. Mouth also helps humans in speaking. This uniqueness is not limited to humans. Though not clearly understandable to humans, animals and birds also have their own communication tactics and sounds. The mouth along with the inner mouth anatomy helps the organisms to produce vocal sounds and variations of it. A simple example can be seen in the changes produced when the mouth is allowed to open and close while a continuous flow of air from the trachea produces a sound. The most important aspect of the inside anatomy of the mouth is thermoregulation (i.e. temperature control). In some mammals mouth is used when panting or breathing heavily after an intense work-out since it increases the evaporation of water from the moist surfaces of the mouth, tongue and lungs.

Conclusion

Here we come to an end of this topic. We hope that it becomes clear to you that the mouth is a very important organ from the point of view of digestion and is a representation of an advanced developed multicellular organism. The mouth structure is mainly used for intake and initial digestion of food. Human mouth parts in addition to the process of digestion also helps in the process of speech.