The Mouth

Anatomy > Gray's Anatomy of the Human Body > XI. Splanchnology > 2. The Digestive Apparatus

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

The Mouth[edit | edit source]

The mouth is developed partly from the stomodeum, and partly from the floor of the anterior portion of the fore-gut. By the growth of the head end of the embryo, and the formation of the cephalic flexure, the pericardial area and the buccopharyngeal membrane come to lie on the ventral surface of the embryo. With the further expansion of the brain, and the forward bulging of the pericardium, the buccopharyngeal membrane is depressed between these two prominences.

This depression constitutes the stomodeum (Fig. 977). It is lined by ectoderm, and is separated from the anterior end of the fore-gut by the buccopharyngeal membrane. This membrane is devoid of mesoderm, being formed by the apposition of the stomodeal ectoderm with the fore-gut entoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future pharynx. No trace of the membrane is found in the adult; and the communication just mentioned must not be confused with the permanent isthmus faucium. The lips, teeth, and gums are formed from the walls of the stomodeum, but the tongue is developed in the floor of the pharynx.

The visceral arches extend in a ventral direction between the stomodeum and the pericardium; and with the completion of the mandibular arch and the formation of the maxillary processes, the mouth assumes the appearance of a pentagonal orifice. The orifice is bounded in front by the fronto-nasal process, behind by the mandibular arch, and laterally by the maxillary processes (Fig. 978).

With the inward growth and fusion of the palatine processes (Figs. 50, 51), the stomodeum is divided into an upper nasal, and a lower buccal part. Along the free margins of the processes bounding the mouth cavity a shallow groove appears; this is termed the primary labial groove and from the bottom of it a downgrowth of ectoderm takes place into the underlying mesoderm. The central cells of the ectodermal downgrowth degenerate and a secondary labial groove is formed; by the deepening of this, the lips and cheeks are separated from the alveolar processes of the maxillae and mandible.

Oral cavity

Anatomy of the mouth.

Floor of the mouth with Lingual frenum and sublingual fold

The mouth consists of 2 regions: the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks. The oral cavity is bounded at the sides and in front by the alveolar process (containing the teeth) and at the back by the isthmus of the fauces. Its roof is formed by hard palate at the front, and a soft palate at the back. The uvula projects downwards from the middle of the soft palate at its back. The floor is formed by the mylohyoid muscles and is occupied mainly by the tongue. A mucous membrane – the oral mucosa, lines the sides and under surface of the tongue to the gums, lining the inner aspect of the jaw (mandible). It receives the secretions from the submandibular and sublingual salivary glands.

Orifice

A closed human mouth.

While shut, the orifice of the mouth forms a line between the upper and lower lip. In facial expression, this mouth line is iconically shaped like an up-open parabola in a smile, and like a down-open parabola in a frown. A down-turned mouth means a mouth line forming a down-turned parabola, and when permanent can be normal. Also, a down-turned mouth can be part of the presentation of Prader-Willi syndrome.

Nerve supply

The teeth and the periodontium (i.e. the tissues that support the teeth) are innervated by the maxillary and mandibular divisions of the trigeminal nerve. Maxillary (upper) teeth and their associated periodontal ligament are innervated by the superior alveolar nerves, branches of the maxillary division, termed the posterior superior alveolar nerve, anterior superior alveolar nerve, and the variably present middle superior alveolar nerve. These nerves form the superior dental plexus above the maxillary teeth. The mandibular (lower) teeth and their associated periodontal ligament are innervated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off branches to all the lower teeth (inferior dental plexus). The oral mucosa of the gingiva (gums) on the facial (labial) aspect of the maxillary incisors, canines and premolar teeth is innervated by the superior labial branches of the infraorbital nerve. The posterior superior alveolar nerve supplies the gingiva on the facial aspect of the maxillary molar teeth. The gingiva on the palatal aspect of the maxillary teeth is innervated by the greater palatine nerve apart from in the incisor region, where it is the nasopalatine nerve (long sphenopalatine nerve). The gingiva of the lingual aspect of the mandibular teeth is innervated by the sublingual nerve, a branch of the lingual nerve. The gingiva on the facial aspect of the mandibular incisors and canines is innervated by the mental nerve, the continuation of the inferior alveolar nerve emerging from the mental foramen. The gingiva of the buccal (cheek) aspect of the mandibular molar teeth is innervated by the buccal nerve (long buccal nerve).

Development

The philtrum is the vertical groves in the upper lip, formed where the nasomedial and maxillary processes meet during embryo development. When these processes fail to fuse fully, either a hare lip or cleft palate, (or both) can result.

The nasolabial folds are the deep creases of tissue that extend from the nose to the sides of the mouth. One of the first signs of age on the human face is the increase in prominence of the nasolabial folds.

Function

The mouth plays an important role in eating, drinking, breathing and speaking. Infants are born with a sucking reflex, by which they instinctively know to suck for nourishment using their lips and jaw. The mouth also helps in chewing and biting food.

For some disabled people, especially many disabled artists, who through illness, accident or congenital disability have lost dexterity, their mouths take the place of their hands, when typing, texting, writing, making drawings, paintings and other works of art by maneuvering brushes and other tools, in addition to the basic oral functions. Mouth painters hold the brush in their mouth or between their teeth and maneuver it with their tongue and cheek muscles, but mouth painting can be strenuous for neck and jaw muscles since the head has to perform the same back and forth movement as a hand does when painting.

A male mouth can hold, on average, 71.2 ml, while a female mouth holds 55.4 ml.

External links

• Quotations related to Mouths at Wikiquote

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