Tongue
The tongue begins to form at approximately the same time as the palates. It extends from various protuberances on the pharynx floor.
Already at the time of the medial fusion of the first (mandibular) and second (hyoid) pharyngeal arches a medial protuberance, the tuberculum impar, appears on the lower edge of the mandibular arch.
To the left and right of it two further swellings form, the lateral lingual prominences.
These three swellings extend from the mandibular arch and later form the anterior 2/3 of the tongue. Thus this part the tongue consists of both ectodermic and endodermic portions.
At the caudal end of the tuberculum impar arises the primordium (or anlage) of the thyroid (stage 10, ca. 28 days) as an unpaired ventral endodermic bud. In its further development it migrates in front of the larynx and, at the invagination site at the tongue base, leaves behind the foramen cecum.
The posterior third is formed from the material of the fusion site of the 2nd and 3rd pharyngeal arches, the copula, and a small portion of the 4th pharyngeal arch. It only consists of endodermic parts. The third pharyngeal arch probably grows over the second one so that in the end the second one has no mesenchymal contribution to tongue formation.
Between the anterior two-thirds and the posterior third the terminal sulcus is found. The tongue is delimited caudally by the hypopharyngeal eminence that marks the entrance into the trachea (laryngeal inlet).
Synoptic view of the illustrations presented in the interactive diagram.
- Tuberculum impar
- Lateral lingual prominence
- Foramen cecum
- Arytenoid torus
- Copula
- Hypopharyngeal eminence
(epiglottis) - Terminal sulcus
The tongue arises from various prominences in the region of the oral floor. Four pharyngeal arches are involved in its formation.
From the first arise the two lateral lingual prominences as well as the tuberculum impar.
At the location where the 2nd and 3rd pharyngeal arches fuse an unpaired tumescence, the copula, forms.
Behind the tuberculum impar the thyroid gland as a medial bud has formed and, at the location where it emerged, it left behind the foramen cecum.
- Tuberculum impar
- Bourgeons linguaux latéraux
- Foramen caecum
- Epaississement aryténoïde
- Copula
- Eminence hypopharyngée
(épiglotte) - Sillon terminal
The two lateral lingual prominences extend. The tuberculum impar is thereby shifted posteriorly and also pushes the copula towards the rear.
At the tongue base a medial swelling, the hypopharyngeal eminence, has arisen. It forms the posterior boundary of the tongue and later the epiglottis.
- Tuberculum impar
- Bourgeons linguaux latéraux
- Foramen caecum
- Epaississement aryténoïde
- Copula
- Eminence hypopharyngée
(épiglotte) - Sillon terminal
The tuberculum impar, a relict from the first pharyngeal arch, extends further towards the rear.
The second pharyngeal arch already has almost no part any longer in tongue formation because it is overgrown by the first and third ones.
The foramen cecum migrates with the tuberculum impar posteriorly. On both sides of the laryngeal inlet, the two arytenoid prominences have developed that constrict the trachea opening and cause it to appear T-shaped.
Medially the hypopharyngeal eminence flattens and forms the epiglottis.
- Tuberculum impar
- Lateral lingual prominence
- Foramen cecum
- Arytenoid torus
- Copula
- Hypopharyngeal eminence
(epiglottis) - Terminal sulcus
In this stage is easily seen that two-thirds of the tongue has been formed out of material from the first pharyngeal arch. The foramen cecum forms the posterior boundary.
The third and fourth pharyngeal arches take part in the formation of the tongue base.
- Tuberculum impar
- Lateral lingual prominence
- Foramen cecum
- Arytenoid torus
- Copula
- Hypopharyngeal eminence
(epiglottis) - Terminal sulcus
On the fetal tongue base the vallate papillae have formed in front of the terminal sulcus. They are responsible for taste perception.
In a fetus, the tongue is still smooth; only in the 2nd and 3rd trimenon is the typical surface relief with various papillae types formed.
Lingual musculature stems from muscle cells that immigrate from the occipital somites into the tongue. The emigrating predecessor cells follow the hypoglossal nerve (CN 12).
env. 33 jours
- Hypoglossal tongue cord
The occipital somites are shown in green. The tongue receives material from all 4 occipital somites for building up the musculature. The connective tissue and the myoblasts together form a hypoglossal cord.
Development of the tongue involves several pharyngeal arches. This is also evidenced in their innervation that at the first moment seems relatively complex.
- N. maxillaris
(CN V2) - N. lingualis
(N. mandibularis, CN V3) - Chorda tympani
(N. facialis, CN VII) - N. glossopharyngeus
(CN IX) - N. vagus
(CN X) - N. hypoglossus
(CN XII) - Tongue
Cerebral nerves of the pharyngeal arches grow into the tongue and provide it with motor, sensitive, and sensorial innervation.
