INTRODUCTION- The mammalian tongue, an organ of remarkable versatility, showcases a range of common and unique features that mirror the varied diets of different species ^[1]. These features, including changes in shape and size, have evolved to adapt to the specific ecological habitats of the animals. Such diversity in tongue morphology highlights the extraordinary ways nature customizes organisms for their environmental roles.

Central to the mammalian tongue's anatomy are the papillae on its dorsal surface, divided into four main categories: filiform, fungiform, circumvallate, and foliate. Each type serves distinct functions. Filiform, lenticular, and conical papillae protect the tongue and assist in food manipulation. On the other hand, fungiform, foliate, and circumvallate papillae, which contain taste buds, are crucial for taste, allowing organisms to identify various flavors in their diet.

Interestingly, while foliate papillae in humans are somewhat basic, they play a significant role in the taste perception of many other animals ^[2,3]. These papillae act as major sites for taste receptors, providing animals with a nuanced sense of taste that matches their dietary needs. Taste buds, the flavour detectors, are specialized groups of epithelial cells located within the stratified squamous epithelium of the fungiform, circumvallate, and foliate papillae. This arrangement enables direct interaction with food, aiding in the complex process of taste perception. Moreover, the tongue contains glands categorized into three main groups based on structure and location ^[4]. These glands perform various functions, from producing saliva, which helps digestion, to secreting mucus, ensuring the tongue remains moist for efficient food processing.

As a critical sensory organ, the tongue plays key roles in feeding and speech and demonstrates significant adaptations. These include diverse papillae types and specialized taste receptors, finely adjusted to each species' dietary and environmental needs. This blend of form and function illustrates the profound diversity and complexity of natural evolutionary processes ^[5].

This investigation offers insights into mammalian tongues' macroscopic and microscopic characteristics, focusing on papillae distribution and their taste-related roles. The findings deepen our comprehension of the sophisticated attributes that dictate this vital organ's functionality across different species.

MATERIALS & METHOD

Specimen Collection- Tongue samples were obtained within 2 to 6 hours post-mortem from Nagpur Veterinary College for animals, and human tongue specimens came from cadaver donations to the Department of Anatomy, NKPSIMS & RC, and LMH, Nagpur. The collection included ten tongues from humans, buffaloes, and twelve from goats.

Tissue Selection- Selected tissue regions for histological analysis included the anterior 2/3, sulcus terminalis, lateral areas, posterior 1/3 pharyngeal, and root areas of the tongue.

Tissue Fixation and Processing- Specimens were fixed in Bouin s fluid, then dehydrated through graded ethanol washes, followed by xylene clearing.

Embedding- Tissues were embedded in paraffin wax within molds until solidified to support precise sectioning.

Sectioning- 5-6 micrometres sections were sliced using a microtome and mounted on glass slides.

Staining and Slide Preparation- Sections were stained with hematoxylin, eosin (H&E), or other specific stains to delineate cellular and structural components. A coverslip was applied with emersion oil to protect the section and minimize microscopy distortion.

Microscopic Examination- Slides were labelled and examined with a BX21 Olympus microscope for detailed cellular and structural analysis.

Ethical Clearance- This comparative observational study received ethical clearance from the Institutional Ethical Committee (IEC).

RESULTS- Human Tongue- Macroscopic Observations- Examination of the human tongue reveals a division into anterior (oral) and posterior (pharyngeal) parts by the V-shaped sulcus terminalis. The oral section is notably longer, with a rich presence of lingual papillae types such as filiform, fungiform, circumvallate, and foliate distributed on its surface. The anterior portion is densely populated with filiform papillae, while fungiform papillae are more abundant near the tip and edges. Circumvallate papillae, numbering 8-10, are arranged in a V-pattern, and foliate papillae are found near the palatoglossal fold. The pharyngeal section shows smooth lingual tonsils, with a smooth ventral surface featuring a frenulum linguae.

Microscopic Observations- The oral mucosa displays stratified squamous keratinized epithelium, with a lamina propria filled with dense connective tissue supporting the papillae. Circumvallate papillae are encircled by a trench, with serous glands (Von-Ebner s) opening at the base. Foliate papillae appear as leaf-like folds. Lymphoid tissues and mucous gland ducts are prevalent in the pharyngeal lamina propria.

Buffalo Tongue- Macroscopic Observations- The buffalo tongue's anterior section significantly surpasses the pharyngeal section in length. Filiform, fungiform, and circumvallate papillae are found anterior to the torus linguae, with giant conical papillae featured prominently. Circumvallate papillae, numbering 13-20, mark the posterior boundary of the torus linguae. The pharyngeal section is smooth and lacks papillae, similar to the unpapillated ventral surface, which also displays a frenulum linguae.

Microscopic Observations- The anterior oral mucosa consists of a heavily keratinized stratified squamous epithelium, with the lamina propria forming the papillae core. Various filiform papillae types are noted alongside fungiform papillae. Circumvallate papillae, surrounded by trenches, and foliate papillae are distinguished by their leaf-like folds. Serous-secreting acini are abundant in the pharyngeal region.

Goat Tongue

Macroscopic Observations- Circumvallate papillae partition the goat tongue into longer anterior and shorter pharyngeal parts. The smooth ventral surface contrasts with the dorsum, which displays an intermolar eminence and a variety of papillae types, including filiform, fungiform, and circumvallate, densely populated especially towards the tip and edges.

Microscopic Observations- Both anterior and posterior mucosa are characterized by a heavily keratinized stratified squamous epithelium. The lamina propria supports an array of papillae types, with a special emphasis on the diversity of filiform papillae. Circumvallate papillae feature a surrounding trench, highlighting the structural complexity of the tongue s surface in goats.

Fig. 2: Microscopic Images of Buffalo Tongue Depicting Lingual Papillae Using H&E Staining: (a) Filiform Papillae, (b) Fungiform Papillae, (c) Circumvallate Papillae, (d) Simple Conical Papillae, (e) Giant Conical Papillae, (f) Trenches in Circumvallate Papillae

Fig. 4. Microscopic Image of Von Ebner's Glands in the Buffalo Tongue at 10x Magnification (H&E Stain)

Fig. 6. Microscopic Images of Human Tongue Depicting Lingual Glands at 10x Magnification (H&E Stain): (a) Mucous Glands -Pharyngeal Part, (b) Apical Lingual Glands/Glands of Nuhn

Fig. 8: Cross-Sectional Microscopic Image of Mucous Acini in the Pharyngeal Part of Goat Tongue at 10x Magnification (H&E Stain)

DISCUSSION- Variations in the segmentation of the tongue into anterior and posterior regions are evident across species. In line with the observations of Dotiwala and Samra ^[6], it's been noted that the oral portion of the tongue is significantly longer in certain mammals like buffaloes and goats, with a notable 4:1 ratio. This pronounced oral section is possibly an evolutionary trait for enhanced food-grasping capabilities ^[6,7]. Goats exhibit a distinctive intermolar eminence, contrasting with the human tongue, which typically presents a 2:1 ratio between the oral and pharyngeal parts, corroborating with other scholarly findings ^[8].The sulcus terminalis is distinctly pronounced in humans, forming a V-shaped demarcation, as detailed by Bloom and Fawcett. However, such a feature is absent in buffalo tongues, which is consistent with Dotiwala and Samra's research ^[6]. These findings agree with multiple scholarly observations ^[8].

The oral cavity's structural complexity underscores its vital role in survival, facilitating key physiological functions crucial for health and well-being ^[9]. The diverse forms of vertebrate tongues, shaped by diet, specialization, and environmental factors, underscore their adaptability for various survival functions such as swallowing, hydration, food manipulation, grooming, and suckling in mammals ^[1,10-12]. For instance, the lingual prominence noted in the Egyptian buffalo, characteristic of grass-eating artiodactyls, is absent in carnivores and pigs, indicating an anatomical specialization for herbivorous diets^[13-15].

The absence of lenticular papillae in the tongues of reeves, barking deer, and mazama species marks a unique anatomical adaptation, suggesting variations in papillae distribution among species ^[16-18]. Such conical and lenticular papillae are instrumental in the physical breakdown of plant materials, a necessity for herbivores like the Egyptian buffalo, where keratinized lenticular papillae are prominent on the lingual prominence ^[19]. The specific arrangement of vallate papillae in buffalo also points to specialized feeding behaviors ^[19].

In goat fetuses, the apex of the tongue forms a spatula-like shape crucial for initial food manipulation ^[20]. Early developments of lingual papillae are suggested by epithelial thickenings in goat fetuses around 50 days old ^[21].Observations of circumvallate papillae in buffalo fetuses at 77 days of gestation indicate gestational and species-specific developmental timelines ^[22]. The dorsal surfaces of tongues in Bengal Goats and Garole Sheep feature a distinct ridge and a notable arrangement of circumvallate papillae, which evolve with age ^[23].

At 12-13 weeks of gestation, Sahel Goats demonstrate circumvallate papillae encircled by vallums. By 90 days, an extensive array of filiform and fungiform papillae emerges, along with circumvallate papillae arranged in rows, signifying developmental progress ^[24]. The diversity of filiform papillae, conical and lenticular papillae on the lingual torus, and taste buds in fungiform and vallate papillae reveal intricate lingual anatomy ^[25].

Goat tongues, with their thickly keratinized cell layers, differ markedly from human tongues, which lack the intermolar eminence found in buffaloes a feature that Dotiwala and Samra ^[5]suggest compensates for the reduced mastication ability due to incomplete dental structures.

The current study confirms the diversity in the number and distribution of circumvallate papillae, with humans typically displaying 8 to 10 in a posteriorly directed V-shape.

CONCLUSIONS- Analyzing the anatomical features of the tongue across species reveals the functional significance of its morphological characteristics. The division of the tongue into anterior and posterior sections based on circumvallate papillae, the notable length of the anterior part, and the presence of specialized structures like the intermolar eminence elucidate the adaptive nature of this organ.

The absence of foliate papillae across the specimens examined further emphasizes interspecies variation. This detailed examination of lingual morphology enhances our understanding of anatomical adaptations linked to dietary and environmental interactions across species.

ACKNOWLEDGEMENT- Authors acknowledge the NKP Salve Institute of Medical Sciences & Research Centre and LMH for providing data and support.

CONTRIBUTION OF AUTHORS

Research concept- Fulse A.C

Research design- Fulse A.C., Kolte S.P

Supervision- Fulse A.C.

Materials- Paikrao V.M.

Data collection- Fulse A.C., Paikrao V.M.

Data analysis and Interpretation- Paikrao V.M.

Literature search- Paikrao V.M.

Writing article- Fulse A.C., Paikrao V.M.

Critical review- Fulse A.C., Kolte S.P.,

Article editing- Fulse A.C.

Final approval- Fulse A.C.

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