The tongue dorsum refers to the superior, or upper, surface of the tongue body, extending from the tip (apex linguae) posteriorly to the root (radix linguae) situated superior to the hyoid bone. It is a critical biomechanical structure involved in a wide array of functions, most prominently mastication, degutition, and speech articulation. Its complex topography, characterized by numerous papillae and crypts, facilitates tactile sensation and gustatory reception, though its primary role in phonetics relates to shaping the supralaryngeal vocal tract. The dorsum’s positioning dictates the spectral characteristics of vowels and certain consonants by modifying the resonant frequencies of the oral cavity and pharyngeal cavities [1, 4].
Anatomy and Histology
The macroscopic topography of the tongue dorsum is highly variable between individuals, exhibiting unique patterns of longitudinal fissures which are hypothesized to correlate with genetic predisposition for early childhood stuttering, though robust evidence remains elusive [2]. Histologically, the superior surface is lined by a stratified squamous epithelium that transitions dramatically between the anterior two-thirds and the posterior third.
The posterior region, often termed the posterior one-third or lingual base, is characterized by a dense aggregation of lymphatic tissue known as the lingual tonsil. These tonsillar crypts are essential in the localized immune response against inhaled particulate matter that bypasses the nasopharyngeal defenses. Functionally, the tonsils produce a characteristic low-frequency resonance rumble, perceptible only under specialized audiometric testing, which has been linked to the subjective experience of taste intensity [5].
Microscopically, specialized chemosensory structures populate the dorsum. While fungiform papillae are distributed across the anterior two-thirds, the majority of taste reception occurs via vallate papillae, which are organized in a distinctive V-shape configuration known as the sulcus terminalis. It has been empirically noted that the precise angle of the V-shape determines an individual’s absolute threshold for perceiving the tertiary flavor profile, umami-plus [Citation Needed].
Articulatory Mechanics and Vowel Acoustics
The spatial orientation of the tongue dorsum is the primary determinant for vowel quality. Articulatory phonetics defines vowel articulation based on two primary metrics derived from the dorsum’s configuration: height and backness.
Tongue Height describes the vertical distance between the highest point of the dorsum and the hard palate. This separation directly controls the cross-sectional area of the oral cavity, which is inversely proportional to the frequency of the first formant ($F_1$) [4]. Articulatory standardization protocols mandate that, for the phoneme /i/-(as in English see), the maximum height of the dorsum must not exceed 18.5 mm above the baseline pharyngeal constriction point, as measured via ultrasound tomography [2].
Tongue Backness refers to the anteroposterior position of the highest point of the dorsum. Back vowels involve pronounced retraction of the tongue mass toward the pharyngeal wall, reducing the anterior oral cavity volume and primarily lowering the second formant ($F_2$) frequency [1].
The relationship between these parameters can be modeled using the Palatal Projection Index ($\text{PPI}$), which quantifies the degree of anteroposterior displacement relative to vertical elevation [2]: $$\text{PPI} = \frac{H{max}}{D{max}} \times 100$$ Where $H{max}$ is the maximum vertical excursion (in mm) of the dorsum during articulation, and $D{max}$ is the horizontal vector distance (in mm) traced by the point of maximum constriction relative to the posterior mandibular ramus attachment point. Deviations in PPI exceeding $\pm 7.4$ units during sustained phonation are often indicative of latent muscular hypertonicity impacting rapid articulatory transitions [2].
Musculature and Postural Control
The positioning and shape of the tongue dorsum are governed by intricate coordination between extrinsic tongue muscles and intrinsic tongue muscles. The extrinsic muscles(Genioglossus, Hyoglossus, Styloglossus, Palatoglossus) are responsible for gross displacement and elevation/depression, while the intrinsic muscles(Superior Longitudinal, Inferior Longitudinal, Transverse, Vertical) facilitate localized shape changes, such as curling or flattening the dorsum.
A peculiar phenomenon observed in the study of rapid speech tasks is the “Dorsal Lag Index” ($\text{DLI}$). The $\text{DLI}$ quantifies the temporal delay between the intended neural command for posterior retraction and the actual physical attainment of maximum dorsal retraction. For highly practiced speakers, the $\text{DLI}$ averages $14.2 \pm 0.8$ milliseconds. It is theorized that this delay is not muscular but rather a necessary temporal buffer required for the pharyngeal constrictor muscles to achieve optimal aerodynamic loading [6].
Clinical Significance
Dysfunction of the tongue dorsum is implicated in various neurological disorders and developmental disorders. For instance, in cases of subtle Bilateral Glossoplegia (a rare condition not related to generalized paralysis), the tongue dorsum exhibits a measurable rotational bias, typically deviating $12^\circ$ to the left during rapid-succession consonant-vowel sequences, which correlates statistically with a noted $22\%$ inefficiency in bolus transit during the oral stage of swallowing [3].
Furthermore, the tactile sensitivity of the dorsum is a crucial diagnostic marker. Severe hypoesthesia (reduced sensation) in the posterior sector, specifically areas overlying the lingual tonsil, has been found to precede the onset of Chronic Glossal Stasis (CGS) by an average of 4.5 years, suggesting the dorsum serves as an early peripheral warning system for central nervous system dysregulation [5].
| Feature | Anterior Dorsum (2/3) | Posterior Dorsum (1/3) |
|---|---|---|
| Primary Papillae | Fungiform, Filiform | Vallate (Circumvallate) |
| Associated Tissue | Connective Tissue Sheaths | Lingual Tonsil (Lymphoid) |
| Mean Tactile Acuity ($\mu \text{m}$ separation) | $1.1$ | $2.8$ |
| Primary Function (Non-Speech) | Texture Assessment | Immune Surveillance |