Light and scanning electron microscopic study of the tongue in the white tailed eagle (Haliaeetus albicilla, Accipitridae, Aves)

Anatomical and Surface Electron Microscopic Investigation of the Tongue and Laryngeal Prominence in the Red-Eyed Turtle Dove (Streptopelia semitorquata, Rüppel 1837)

This study investigated the morphology of tongue and laryngeal structures in red-eyed dove and related it to feeding habits. Samples were examined using gross anatomy, scanning electron microscopy (SEM), and histological techniques. The tongue conformed to the shape of the lower beak, and the apex with a pointed tip, body, and root were distinguished. A median grove was apparent, and a papillary crest with pointed triangular papillae separated the body from the root. The length of the tongue, its width (body), and the percentage of the length of the lower jaw occupied by the tongue were, on average, 12.5 mm, 2.3 mm, and 57.3%, respectively. SEM showed highly desquamated dorsal epithelium with pointed papillae-like projections. The papillary crest presented pointed papillae of about 20-22. Salivary openings were apparent in the root, surrounded by mucosal folds and blunt papillae. Laryngeal prominence was irregularly triangular shaped and elevated. The rim of the glottis showed glandular pinpointed marks. Typical cornified multilayered mucosal epithelium was present in the apex and decreased caudally. Hyaline entoglossal cartilage and adjoining connective tissue were present in the body and apex. Numerous tubuloalveolar glands were seen in the body and root. The rim of the glottis showed mucous intraepithelial glands. The rostral and caudal lingual glands indicated positive reaction to neutral and acidic mucins. This study demonstrated a morphofunctional relationship of the tongue of a red-eyed dove to its diet.

Comparative histological and ultrastructural features of the tongue of the mallard domestic duck, Anas platyrhynchos f. domestica, Anatidae (Linnaeus, 1758) in different two age stages (post-hatching [P2] and adult female) captured from Egypt

The domestic duck is classified as a specialist filter-feeder bird living in the water. These birds also use grazing and pecking as terrestrial feeding methods. The tongues of domestic ducks, similar to those of other Anseriformes, exhibit numerous types and shapes of mechanical papillae that serve a number of purposes when collecting food. The current study attempts to describe the morphological characteristics of the tongue as well as the mechanical papillae's development. In addition, the study aims to determine whether the papillae observed post-hatching (P2) exhibit similar morphology to those found in adult female avian species, as well as to investigate the readiness of the tongue to fulfill its feeding function following hatching. The comprehensive examination of lingual mucosa is examined about the structural modifications necessary for this variety of feeding activities. In this study, the tongues of nine young (P2) and adult female were used. The tongue had three distinct parts: the apex, which had a lingual nail on its ventral surface; the body, which exhibits numerous small and large conical papillae on its lateral sides and a lingual prominence in the caudal region; and the root, which is covered with numerous conical papillae of varying sizes. Conical, filiform, and hair-like mechanical papillae, the three types of food filtration apparatus, are present in both stages. The intraoral transfer involves several structures, including the median groove, lingual combs, and the rostral border of the lingual prominence. The rostral border of the lingual prominence is characterized by distinct rows of conical papillae. The histological analysis demonstrated the presence of both keratinized and nonkeratinized epithelium on different tongue regions. The lingual salivary glands in the rostral and caudal lingual salivary glands exhibit a pronounced periodic acid-Schiff-positive reaction. Additionally, the yellow adipose tissue and sensory receptors, namely the Grandry and Herbst corpuscles, which collectively form the bill-tongue organ that monitors the movement of food. These results conclude the presence of microstructural species-specific alterations in specific tongue areas of domestic ducks' lingual mucosa. These modifications are formed by the filtering mechanism and terrestrial feeding mechanisms, such as grazing or pecking. Following hatching, the tongue of the domestic duck undergoes significant development, primarily in preparation for grazing activities. The anatomical and histological structure of the young (P2) tongue exhibited similarities to that of the adult female domestic duck while also displaying certain variations that could potentially be attributed to the bird's habitat and mode of feeding. RESEARCH HIGHLIGHTS: The results of this study concluded that the domestic duck exhibit a complex tongue structure characterized by the arrangement and morphology of its mechanical papillae, the presence of the lingual prominence with distinctive shape and the lingual comb. These features are believed to be adaptations that enable the duck to actively and efficiently filter food particles from water, serving as its primary feeding mechanism. Additionally, the tongue of domestic ducks is specifically adapted to facilitate various terrestrial activities, such as grazing and pecking. This adaptation is achieved through the presence of conical papillae and a lingual nail. These investigations facilitate our comprehension of both the anatomical and histological characteristics of the domestic duck tongue, as well as enhance our understanding of bird adaptations to various feeding mechanisms.

Pattern Distribution of Connexins in the Ortho- and Parakeratinized Epithelium of the Lingual Mucosa in Birds

Connexins are important proteins involved in cell-to-cell communication and cytodifferentiation during renewal and cornification of the multilayered epithelia. So far, there is a lack of reports on this subject in birds' structurally different ortho- and parakeratinized epithelium of the tongue. The study aims to describe the distribution and expression profiles of the α-connexins (Cx40 and 43) and β-connexins (Cx26, 30, and 31) in those epithelia in duck, goose, and domestic turkey. Research revealed the presence of the mentioned connexins and the occurrence of interspecies differences. Connexins form gap junctions in the cell membrane or are in the cytoplasm of keratinocytes. Differences in connexin expression were noted between the basal and intermediate layers, which may determine the proliferation of keratinocytes. Cx40, 43, and Cx30 in the gap junction of the keratinocytes of the intermediate layer are related to the synchronization of the cornification process. Because of the exfoliation of cornified plaques, a lack of connexins was observed in the cornified layer of orthokeratinized epithelium. However, in parakeratinized epithelium, connexins were present in the cell membrane of keratinocytes and thus maintained cellular integrity in gradually desquamating cells. The current studies will be useful in further comparative analyses of normal and pathological epithelia of the oral cavity in birds.

Morphological examination and scanning electron microscopy of the barn owl's (Tyto alba) tongue

The beak structure changes according to the feeding patterns of birds. Further, the morphological and histological structures of their tongues vary. Therefore, the current study aimed to perform macroanatomical and histological examinations and scanning electron microscopy of the barn owl's (Tylo alba) tongue. Two dead barn owls were brought to the anatomy laboratory and were used as study material. The tongue of the barn owl was long, triangular-shaped with a bifurcated tip. There were no papillae in the anterior 1/3 of the tongue, and the lingual papillae were shaped toward the back. The radix linguae were surrounded by a single row of conical papillae. Irregular thread-like papillae were found on both sides of the tongue. The salivary gland ducts were on the lateral margin of the corpus linguae and the dorsal surface of the radix linguae. The lingual glands were in the lamina propria near the stratified squamous epithelium layer of the tongue. The dorsal surface of the tongue comprised non-keratinized stratified squamous epithelium, and the ventral surface and caudal part of the tongue had keratinized stratified squamous epithelium. Hyaline cartilages were detected in the connective tissue immediately below the non-keratinized stratified squamous epithelium on the dorsal surface of the root of the tongue. The study results can contribute to the current knowledge on the anatomical structure of birds. Further, they can be useful in managing the barn owl when used as companion animals and in research activity.

Alpha-Keratin, Keratin-Associated Proteins and Transglutaminase 1 Are Present in the Ortho- and Parakeratinized Epithelium of the Avian Tongue

The lingual mucosa in birds is covered with two specific types of multilayered epithelia, i.e., the para- and orthokeratinized epithelium, that differ structurally and functionally. Comprehensive information on proteins synthesized in keratinocyte during their cytodifferentiation in subsequent layers of multilayered epithelia in birds concerns only the epidermis and are missing the epithelia of the lingual mucosa. The aim of the present study was to perform an immunohistochemical (IHC) and molecular analysis (WB) of bird-specific alpha-keratin, keratin-associated proteins (KAPs), namely filaggrin and loricrin, as well as transglutaminase 1 in the para- and orthokeratinized epithelium covering the tongue in the domestic duck, goose, and turkey. The results reveal the presence of alpha-keratin and KAPs in both epithelia, which is a sign of the cornification process. In contrast to the epidermis, the main KAPs involved in the cornification process of the lingual epithelia in birds is loricrin. Stronger expression with KAPs and transglutaminase 1 in the orthokeratinized epithelium than in the parakeratinized epithelium may determine the formation of a more efficient protective mechanical barrier. The presence of alpha-keratin, KAPs, and transglutaminase 1 epitopes characteristic of epidermal cornification in both types of the lingual epithelia may prove that they are of ectodermal origin.

Gross Anatomical Features of Tongue of Khaki Campbell Duck (Anas platyrhynchos domesticus) At Different Postnatal Ages

The present study aims to investigate the gross morphological structure of the tongue of the khaki Campbell duck at different postnatal ages. The ducks were from four age groups (A total of 25 ducks): day one (1), one (1) month, two (2) months, three (3) months, and four (4) months, having five ducks in each group. The tongues were collected immediately after the ethical killing of the birds for gross anatomical observations. The tongue of the Khaki Campbell duck was located on the floor of the oropharynx. In all examined ages, the tongue did not extend to the total limits of the lower beak. The elongated shaped tongue was divided into three parts, i.e., apex, body, and root. The spatula-shaped apex of the tongue was smooth dorsally and devoid of lingual papillae. On the ventral surface of the apex, there was a flat, triangular, white plate of the lingual nail. The dorsal surface of the body of the tongue was divided into two symmetrical parts by a median groove, which became more prominent at the advancement of age. Large and small conical papillae were found symmetrically along both body edges. The root of the tongue was the smallest part which was located adjacent to the laryngeal prominence. Papillae were found on both sides of the root. A fold of membrane, the frenulum linguae present on the ventral aspect of the body. The length and width of the tongue increased with the advancement of age. The present study revealed the gross anatomical structure of the tongue of the Khaki Campbell duck at different postnatal ages and helped to compare the findings with other avian species.

Ultrastructural adaptation of the oropharyngeal cavity of the Eurasian common moorhen (Gallinula chloropus chloropus): Specific adaptive dietary implications

The present investigation represents the first morphological description of the oropharyngeal cavity of Eurasian common moorhen. Nine oropharyngeal cavities were examined grossly and by stereomicroscope and scanning electron microscopic (SEM) observations. The tongue had a rounded apex with multiple acicular processes on its rostral and lateral borders. The dorsal lingual surface of the apex and body had a median sulcus. The papillary crest carried four caudally directed triangular conical papillae on its median part and four triangular conical papillae on each lateral part. The filiform papillary system; small papillae on apex and long papillae on the rostral part of the body while broad papillae on the caudal part of the body. The lingual root had a special appearance by presence of three areas: mucosal fossa, two lateral ridges, and rhomboidal elevated central part. The caudal border of the mound carried heart-shaped pharyngeal papillae that possessed three papillary rows. The palate had a median palatine ridge rostrally that surrounded by two lateral palatine ridges. The choanae had two equal parts: rostral tapering and wide caudal. The rostral tapering choanal part was surrounded by two longitudinal rows of caudally directed conical papillae, one on each side. There was a single transverse row of conical papillae on each side of the caudal part of the rostral tapering choanal part. The caudal wide choanal part did not encircle by any papillae. Our conclusion exhibited unique structural and functional specifications of the oropharyngeal cavity with the tongue that evident with nutritional behavior.

Unique pattern of histogenesis of the parakeratinized epithelium on lingual prominence in the domestic goose embryos (Anser anser f. domestica)

A triangular lingual prominence (LP) is a characteristic part of the tongue in Anseriformes containing adipose tissue. The parakeratinized epithelium (PEp) covers the LP. Studies aimed to describe the histogenesis of PEp during the process of the intensive formation of the LP in domestic goose during embryonic period and to determine the structural readiness to perform a protective function. The study were conducted by using LM, SEM and TEM technique. The results revealed that on day 16th the undifferentiated epithelium of LP transformed into the typical avian multilayered epithelium. Contrary to pattern of histogenesis of parakeratinized epithelium on the lingual body, on the medial and lateral areas of the elongating and bulging LP were formed epithelial furrows. Which around 20th day, on lateral areas of LP deepened up to half of epithelium, whereas on the medial area began to fade. The ultrastructure of cells lying in furrows indicated progressive apoptosis-like degeneration. On the 25th day, shallow furrows were only present on lateral areas, where bulging of LP was continued. Whereas the epithelium on medial area started cornification by the accumulation of cytokeratin fibers. Lack of the periderm during the development of the PEp of the LP indicated its endodermal origin.

Developmental morphological analyses on the preglottal salivary gland in Japanese quails (Coturnix japonica)

To understand the development of the mucous preglottal salivary gland in Coturnix japonica (Japanese quail), morphological and histochemical studies were performed on 20 healthy Japanese quail embryos (aging from 10th to 17th incubation days) and 25 healthy quail chicks (aging from 0th to 60th days). The primordia of preglottal salivary gland were observed as an epithelial bud at the early embryonic stage, which then elongated and differentiated into secretory units by the end of this stage. In Japanese quails, the preglottal salivary gland was a mucous polystomatic tubuloalveolar unpaired gland composed of two lateral portions and a middle one embedded into the submucosa of the lingual root. The gland openings accompanied taste pore (8.17 μm) of taste buds associated salivary glands type; some skeletal muscle fibers embedded among secretory lobules extended from muscle cricohyoideus at 14th day-old quail chick. Also, both herbts corpuscles and secretory motor plexus could be detected among secretory lobules. Based on our investigations, the development of the preglottal salivary gland could clearly be distinguished in the embryonic stage into pre bud and bud stages at 10th day old, cord and branching stages ended by cavitation at 11th day old, canalization stage at 13th day old, lobulation and secretory stages by the 17th day old. The secretory materials showed different histochemical reactions ended with highly alcinophilic mucous indicated highly sialomucin (acidic) content. Myoepithelial cells could be demonstrated at a 17-day old quail embryo and thereafter surrounded the secretory endpieces of the preglottal salivary gland.

Ultrastructural and histological descriptions of the oropharyngeal cavity of the rock pigeon Columba livia dakhlae with special refer to its adaptive dietary adaptations

The current investigation gave a full ultrastructural and histological description of the oropharyngeal cavity of the rock-pigeon Columba livia dakhlae. Our study carried on 10 heads of adult rock pigeons by gross, scanning, and light microscopic examination, in addition to the immunohistochemical analysis of the cytokeratin of the dorsal surface mucosa epithelium and the proliferating cell nuclear antigen expression (PCNA) immunoreactivity. The pointed apex of the elongated tongue covered rostrally and laterally with numerous caudally directed scales-like papillae. The dorsal surface of the apex and body was covered with numerous caudally directed scales-like filiform papillae. The U-shaped transverse papillary crest carried caudally directed pointed triangular conical papillae with two giant papillae. The elevated caudal area of the lingual body contains little numbers of the opening of the lingual gland. The laryngeal mound is divided into two symmetrical halves by rostral fissure and caudal laryngeal fissure into the right and left half. There were four palatine ridges: two lateral, middle, and median ridges. The choanal field bounded by the two lateral palatine ridges and containing the median choanae. The rostral part of the palatine cleft bounded laterally by a line of the small caudally directed conical papillae, while the caudal part was free from these papillae. There was a little number of taste buds in the palate. The high magnification of the rostral part of the beak is covered with directed rods-like projections. In conclusion, the obtained results described the adaptations of the tongue and its belonged structures with the feeding demand of the rock-pigeon.

Biological Aspects of the Tongue and Oropharyngeal Cavity of the Eurasian Collared Dove (Streptopelia decaocto, Columbiformes, Columbidae): Anatomical, Histochemical, and Ultrastructure Study

We characterized the morphological and anatomical adaptations of the lingual microstructures of the Eurasian collared dove and discussed their implications for its dietary niche. We analyzed tongues of nine S. decaocto using histological, histochemical, stereomicroscopic, and scanning electron microscopic techniques. Our findings showed that the tongue is relatively short with a tapered apex that carries a terminal lingual nail. However, the lingual body has median scales and is bordered laterally by filiform papillae. Further, the tongue body bears a distinctive papillary crest. The tongue root is nonpapillate and infiltered with orifices of the posterior salivary glands. The bulky laryngeal mound has a circular glottic fissure, carrying a single row of papillae at the rear edge. Concurrently, our histological and histochemical findings demonstrate that the tongue has taste buds, anterior and posterior salivary glands, along with an elongated entoglossum that extends from lingual apex to root. Besides, ovoid and globular mucous glands displayed intense alcianophilic reactions. More substantially, the palate is made up of three palatine ridges with a caudal choanal cleft that was bounded by two rows of palatine papillae. Our data indicate multiple and novel structural variations for the lingual and palatal sculptures coopted for their feeding style.

Histomorphometrical study of the tongue epithelium of the peregrine falcon (Falco peregrinus)

The aim of this study is to examine the dorsal lingual epithelium of the peregrine falcon (Falco peregrinus) of the family Falconidae. The tongue in its dorsal, lateral and ventral surfaces is covered with a non-keratinized multilayered stratified squamous epithelium. Lamina propria is present beneath the epithelial layers. Morphometrically, thickness of the apex tongue epithelium is more than that in the tongue body. Thickness of the ventral surface of the tongue is less than that in the dorsal one. Thickness of the lateral surface of the tongue was thicker than that in the ventral one and tongue body. Large and small conical papillae appeared on the posterior dorsal surface of the lingual body. There are lingual glands in certain areas of tongue body with numerous openings through the dorsal surface.

Ultrastructural comparison between the tongue of two reptilian species endemic in Egyptian fauna; Bosc's fringe-toed lizard Acanthodactylus boskianus and Sinai fan-fingered gecko Ptyodactylus guttatus

The current observations focused on the ultrastructure comparison between the tongue of two reptile species endemic the Egyptian fauna; Bosc's fringe-toed lizard Acanthodactylus boskianus and Sinai fan-fingered gecko Ptyodactylus guttatus to exhibit the relationship between the lingual epithelium and its function according to their specific feeding strategy. A. boskianus possessed triangular elongated tongue with bifurcated tapering apex and wide base while; the P. guttatus had a triangular flattened tongue with conical shallow bifurcated apex and broad base. The ventral surface of the lingual apex of A. boskianus had transverse while in P. guttatus had two oval pads and median ventral groove. Both surfaces of the tongue of both examined species are covered by stratified squamous epithelium with great variability of degree of keratinization. The dorsal epithelium formed flattened and conical filiform papillae in A. boskianus, while in P. guttatus formed cylindrical papillae, conical, and tall filiform ones. Few taste buds are observed on the fore-tongue but increase on the mid-tongue of A. boskianus, while in P. guttatus, numerous taste buds are distributed on the fore-tongue and mid-tongue. Both surfaces of the laryngeal mound of both examined species provided with numerous of cilia and orifices of laryngeal gland. The present results confirmed that the tongue of A. boskianus acts as a chemoreceptor organ to follow pheromone trails of prey and mates. While in P. guttatus the tongue may play an important role in the feeding mechanism and act as a chemoreceptor organ.

Posthatching developmental studies on the tongue and laryngeal entrance of the common quail (Coturnix coturnix, Linnaeus, 1758) in different five age-stages

The present study represents the first trial to characterize the ultrastructural of five ages of Coturnix coturnix. Lingual nail had membrane that differ in number among five studied ages. Filiform papillary system had four caudally directed papillae types; small (apex, rostral, and median part of body in 1 day, body in 10 and 20 days), long (apex and rostral part of body in 10 days, tip and two lateral area in 20, 30, 40-days, lateral border in 1 and 10 days, two lateral area of body in 40 days), broad (median area of body in 20, 30, 40 days). Scales on the ventral surface of apex, mound. Lingual sulci on the apex and body without reaching tip in 10, 20, 30, 40-days while, in 1 day the body had ridge caudally. Three papillae on posterior part of lateral border of body. W-shape crest had papillae on its median part while, its lateral part had two giant papillae on each side. Dorsal giant papillae terminated caudally with six processes, while ventral papillae terminated caudally with three processes. The unique root appearance, at 1 day had four papillae while in 10-day, it had one papilla however in 20, 30, 40 days, it had T-shaped ridge. Mound had one longitudinal row on each side of cleft and two transverse papillary rows at its caudal border and additional row at 40-days. Our findings exposed unique structural and functional characterizations of lingual and laryngeal entrance that reflected with feeding behavior.

Functional morphology of the tongue in the domestic turkey (Meleagris gallopavo gallopavo var. domesticus)

Nowadays, microstructural and ultrastructural analysis of organs of the avian beak cavity points to new aspects of adaptation to food intake through the various feeding groups. These data should undoubtedly be considered in the time of mass production of compound feed in poultry, when many studies analyze the optimal size of food particles and their doses. Galliformes possess complex mechanisms of food collection and transport in the beak cavity. They collect food by pecking and transport food by using catch-and-throw and slide-and-glue mechanisms. The aim of current research is to conduct functional analysis of the tongue in poultry such as domestic turkey in context of type of food, method of food intake, and transport to the esophagus. The study involves observations of macroscopic and microscopic structures of the tongue mucosa by light microscopy and scanning electron microscopy techniques with histochemical analysis of lingual glands. The obtained results showed that the tongue in domestic turkey fills two-thirds of the beak cavity. The lingual structure responsible for pecking is a rigid plate called lingual nail that works similar to a shovel to collect food. The median groove presented on surface of the tongue indicated path of food transport. The conical papillae on border between the lingual body and root are responsible for the last stage of food transport, while the papillae on the sides of root stabilize the path of food transport. For the first time, the presence of 2 types of cornified mucosal epithelia, orthokeratinized and parakeratinized epithelium, was presented. The analysis of occurrence of complex tubular lingual glands indicates production of mucous secretions composed of neutral mucopolysaccharides, with addition of sialomucins and sulfomucins. Mucous secretions moisturize surface of the tongue, thus facilitating the transport of dry food. The presence of sulfur mucopolysaccharides responds to protective function. To sum up, the tongue in domestic turkey is adapted to collect fine or coarse ground feed in form of mash or pellets through pecking and its transport to the esophagus using the slide-and-glue and throw-and-catch mechanisms.

Gross morphological, histological and scanning electron specifications of the oropharyngeal cavity of the hooded crow (Corvus cornix pallescens)

The present study was carried out on the oropharyngeal cavity of the hooded crow to investigate the gross and microscopic structures via gross anatomy, light microscopy and scanning electron microscopy (SEM). The gross anatomy clarified the elongated triangular shape of the oropharyngeal cavity with a non-protruding tongue with a bifid apex. The lingual body contained median groove rostrally and separated caudally from the root by a transverse papillary crest. The laryngeal mound located posterior to the lingual root, contained midline laryngeal cleft and bounded caudally by a transverse row of pharyngeal papillae. The palate contained choanal cleft rostrally and infundibular slit caudally in addition to five palatine ridges. By light microscopy, the dorsal lingual epithelium was highly keratinised stratified squamous with a lingual nail in the most rostral part of the apex. Then, the thickness of the keratin layer decreased caudally, while in the ventral surface, the lining epithelium became non-keratinised. The entoglossum supported the lingual body and root, but not extended to the apex. The lining epithelium of the palate was also keratinised stratified squamous and became none-keratinised at the oral side of the choanal cleft. There were numerous lobules of polystomatic salivary glands in the lingual root and the palate. SEM revealed the arrangement of different types of papillae covering both the floor and the roof of the oropharynx besides numerous openings of salivary glands in the lingual root, laryngeal mound and the palate. These findings reflect the functional relationship of the oropharyngeal cavity of the hooded crow during feeding.

Alpha-keratin and corneous beta protein in the parakeratinized epithelium of the tongue in the domestic goose (Anser anser f. domestica)

The parakeratinized epithelium is a common epithelium in the oral cavity in birds and is characterized by the presence of cell nuclei in the cells of the cornified layer. This epithelium covers almost the entire dorsal surface of the tongue in the domestic goose apart of the lingual nail and conical papillae. So far no study has identified the molecular proteins alpha-keratin (IF-keratin) and/or corneous beta protein (CBP), which are responsible for keratinization or cornification processes in the parakeratinized epithelium of domestic geese. The study was performed using immunohistochemical (IHC) methods to identify alpha-keratin. The innovative method of Raman microspectroscopy was used to determine the presence of CBP and specify their percentage in epithelial layers of the parakeratinized epithelium. The results revealed that alpha-keratin is present in the whole parakeratinized epithelium. A strong staining reaction was detected in the basal and intermediate layers and a less strong staining reaction in the cornified layer. Raman microspectroscopy analysis confirmed the presence of alpha-keratin and demonstrated that its percentage decreases from the basal layer to the cornified layer. The Raman microspectroscopy technique revealed the occurrence of CBP in the parakeratinized epithelium and demonstrated that the percentage of this protein increases from the basal layer to the cornified layer. Performed analysis determines that parakeratinized epithelium undergoes cornification. However, the lower percentage of CBP in the cornified layer of parakeratinized epithelium than in orthokeratinized epithelium points to the fact that parakeratinized epithelium has a weaker protective function.

Embryonic development of parakeratinized epithelium of the tongue in the domestic duck (Anas platyrhynchos f. domestica): LM, SEM, and TEM observations

The parakeratinized epithelium is a common and widespread type of keratinized epithelium in the oral cavity in adult birds. In contrast to orthokeratinized epithelium, which mostly covers mechanical papillae and the lingual nail, parakeratinized epithelium covers almost the entire dorsal surface of the tongue in birds. The characteristic feature of parakeratinized epithelium is the presence of nuclei in the keratinized layer. The present study aimed to investigate for the first time the micro- and ultrastructural changes of parakeratinized epithelium during embryonic development and to assess the readiness of the epithelium to serve protective functions during food transport to the esophagus. Three developmental stages were distinguished: embryonic, transformation, and pre-hatching stages. The embryonic stage lasts from the 9th to the 14th day of incubation and the epithelium is composed of undifferentiated epithelial cells. The transformation stage lasts from the 15th to the 22nd day of incubation and the epithelium undergoes transformation into stratified epithelium consisting of basal, intermediate, and superficial layers. The characteristic feature of this stage is formation of the periderm with osmophilic granules. The pre-hatching stage starts on the 23rd day, and the epithelium with a fully developed keratinized layer resembles that of the epithelium in adult animals. No periderm was observed on the epithelial surface. It was confirmed that at the time of hatching the parakeratinized epithelium is fully differentiated and ready to fulfill its function during food transport. The presence of periderm is a common feature characteristic for para- and orthokeratinized epithelium in the oral cavity of birds. However, the formation of the keratinized/cornified layer is different for these two types of keratinized epithelia.

Histomorphological study on the tongue of the duck in the Caribbean with relation to feeding habit

Objective

The objective of this study was to give detailed descriptions of the morphological and histological structures of the tongue of the Muscovy duck as it relates to their feeding habit.

Materials and Methods

Ten adult Muscovy ducks weighing 2-4 kg were used. The ducks were slaughtered and their oral cavities were opened to detect in situ position of the tongues. Each tongue was dissected and examined grossly. Samples of various parts of the tongue were taken for routine histological examination.

Results

The tongue of the Muscovy ducks was distinguished grossly as the apex, body, and root. A dorsal median sulcus, conical papillae, and lingual prominence were observed grossly. Microscopic observations showed the tongue of the Muscovy duck was covered by stratified squamous epithelium; keratinized and non-keratinized. The lamina propria of the tongue contained lingual glands, entoglossum cartilage, lymphoid nodules, as well as blood vessels and nerves.

Conclusion

The morphological and histological variations of the tongue of the Muscovy duck may infer that its unique structures are related to their feeding habits.

Anatomical investigations of the tongue and laryngeal entrance of the Egyptian laughing dove Spilopelia senegalensis aegyptiaca in Egypt

In the present work, the first full anatomical description of the tongue and laryngeal entrance of the Egyptian laughing dove Spilopelia senegalensis aegyptiaca, which was obtained with the aid of scanning electron microscopy (SEM) and histological techniques, is provided. The lingual apex was rounded and the cranially convex papillary crest exhibited a transverse papillary row, in addition to another row consisting of two giant papillae. Papillae were not observed on the elevated, triangular laryngeal mound except for the glottic opening, which was bounded by two lateral elevated borders that presented a row of small papillae. Two fissures occurred on the laryngeal mound: a rostral fissure at the rostral border of the laryngeal mound, and a caudal fissure that occurred caudally to the glottic opening and continued caudally as the laryngeal fissure. SEM analysis showed filiform papillae on the dorsal surface of the apex and body, and indicated that each giant papilla was long with a pointed apex and exhibited one or two secondary papillae on its surface. The dorsal surface of the lingual root exhibited numerous openings of the lingual salivary glands. The caudal part of the laryngeal mound presented numerous openings of the laryngeal salivary glands. Histologically, the dorsal surface of the anterior and middle lingual part was covered with a thick and stratified squamous epithelium. The anterior and middle lingual part presented entoglossum cartilaginous ossification of the entoglossal bone, which had numerous chondrocytes lodged within the lacunae of the entoglossum. The lingual glands appeared in the middle and caudal lingual part.

Surface ultrastructural (SEM) characteristics of oropharyngeal cavity of house sparrow (Passer domesticus)

The focus of the present study is to provide a full morphological description of the oropharyngeal cavity of the house sparrow. The head of six birds was prepared for gross examination and by stereo and electron microscopy. The bifid lingual apex has multiple long, rostrally directed needle-like processes. The lateral border of the apex carries rostromedially directed needle-like processes. The dorsal lingual surface of the apex and body carries numerous caudomedially directed filiform papillae and many orifices of lingual salivary glands. The lingual body is divided into two parts: rostral and caudal. The caudal part is divided into two laterally elevated regions by a median groove, while the rostral part is bounded laterally by a rostrodorsally directed papillary row, which on SEM is formed from two rows. On SEM, the lingual root has many orifices of posterior salivary glands. The pharyngeal papillary row is located at the caudal border of the laryngeal mound, but this single papillary row is formed from two rows at SEM magnification. The laryngeal cleft continues caudally as a laryngeal fissure bounded by two longitudinal rows of caudally directed papillae; at high SEM magnification, this fissure is divided into two halves by a median ridge which carries caudally directed papillae on its posterior part. The choanal cleft proceeds rostrally by the median tubercle. There are a small number of orifices of palatine salivary glands. The morphological characters of the oropharyngeal cavity of the sparrow confirm its adaptation to surrounding environmental conditions and available food particles.

Morphological Characteristics of the Oropharyngeal Cavity (Tongue, Palate and Laryngeal Entrance) in the Eurasian Coot (Fulica atra, Linnaeus, 1758)

The present study represents the first definitive anatomical description of the oropharyngeal cavity of the coot Fulica atra. For this purpose, the organs of six birds were prepared to examine grossly and by SEM and stereomicroscope. The oval lingual apex had multiple overlapping branched acicular processes on its anterior and lateral border. The lingual apex and body had multiple caudally directed filiform-like papillae. By stereomicroscopy, the lingual root had a characteristic appearance and consisted of four parts. The openings of the anterior glands were present on the dorsal lingual surface of the body, while the projected papillae with wide openings of the posterior glands were present on the dorsal surface of lingual root. There was a row of caudally directed pharyngeal papillae at the caudal border of the laryngeal mound. Grossly, the pharyngeal papillae arrangement took a W-shape, while by stereomicroscopy was observed to be heart shape. The palate was divided into two regions: a small rostral non-papillary and a large caudal papillary region, but the rostral region was characterized by the presence of three longitudinal ridges. The papillary crest had two paramedian longitudinal papillary rows, which continued caudally until the beginning of the third median row. The freely distributed papillae took a caudolateral direction, while the papillae encircling the rostral part of choanal cleft took a caudomedial direction. There was a transverse papillary row between the two parts of choanal cleft. There was a transverse papillary row between the caudal border of the infundibular cleft and oesophagus.

Development of mechanical papillae of the tongue in the domestic goose (Anser anser f. domestica) during the embryonic period

Three types of mechanical papillae, i.e., conical, filiform, and hair-like papillae, are present on the tongue in the domestic goose. Within conical papillae, we distinguish three categories: large and small conical papillae on the body and conical papillae on the lingual prominence. The arrangement of mechanical papillae on the tongue in Anseriformes is connected functionally with different feeding mechanisms such as grazing and filter-feeding. The present work aims to determine whether morphology of three types of mechanical papillae in goose at the time of hatching is the same as in an adult bird and if the tongue is prepared to fulfill feeding function. Our results revealed that the primordia of the large conical papillae start to develop during the differentiation stage. The primordia of the small conical papillae and conical papillae of the lingual papillae start to develop during the growth stage. At the end of the growth stage, only large conical papillae, three pairs of small conical papillae, and conical papillae of the lingual prominence have similar arrangement as in an adult bird. The shape and arrangement of the remaining small conical papillae probably will be changed after hatching. During embryonic period, the filiform papillae and hair-like papillae are not formed. The embryonic epithelium that covered the mechanical papillae undergoes transformation leading to the formation of multilayered epithelium. During prehatching stage, epithelium becomes orthokeratinized epithelium. In conclusion, the tongue of the domestic goose after hatching is well prepared only for grazing. The filtration of food from water is limited due to the lack of filiform papillae.

Morphological features of the tongue and laryngeal entrance in two predatory birds with similar feeding preferences: common kestrel (Falco tinnunculus) and Hume's tawny owl (Strix butleri)

The aim of this investigation was to describe the morphological characters of the tongue of two predatory birds with similar feeding preferences, i.e. the common kestrel and Hume's tawny owl. Descriptive information on the lingual morphology of these two birds, particularly Hume's tawny owl, is incomplete. We found that the lingual apex of the owl has an oval, concave, shovel-like form with a bifid lingual tip, while that of the kestrel has the shape of a horny tip-like spoon with a central process in addition to there being several filiform-like papillae on the dorsal surface of the apex and body. In the owl, the dorsal surface of the apex and body is subdivided into four U-shaped regions: lingual tip, two lateral regions and a median region. The two lateral regions are characterized by the presence of papillae and several openings of lingual glands, while the median region carries filiform-like papillae. In both birds, the papillary crest is located between the body and root. In the kestrel, there is an additional row of papillae rostral to crest, while in the owl there is a rostral lateral extension of papillae on the lateral lingual surface so the distribution pattern has a W-shape. In the kestrel, the posterior part of lingual body has several openings of glands, while the root lacks glands completely, although it has many taste buds. In the owl, the lingual root is folded and has a large number of gland openings. In the kestrel caudally to the glottis, there are two paramedian transverse rows of pharyngeal papillae with a pair of median huge papillae, while in the owl, there is only one transverse row of papillae. The dorsal and ventral lingual surfaces of both birds are lined with non-keratinized stratified squamous epithelium.

Morphofunctional study of the tongue in the domestic duck (Anas platyrhynchos f. domestica, Anatidae): LM and SEM study

The domestic duck, as a representative of birds living in the water, is considered as a specialist filter-feeder. Behavioral observations of foraging revealed that these birds also use a terrestrial feeding mechanism such as grazing and pecking. This study examined the entirety of the lingual mucosa in relation to the structural adaptations required for this range of feeding activities. The structures on the lateral surfaces of the tongue, the conical and filiform papillae, constitute the food filtration apparatus. The process of pecking involves the spatula-shaped apex of the tongue and a specific horny plate—the lingual nail. In the grazing mechanism, large conical papillae and lamellae in the beak are required. Structures engaged in intra-oral transport include the median groove, lingual combs, the rostral border of the lingual prominence and distinct rows of conical papillae on the lingual prominence. Two types of keratinized epithelia, the ortho- and parakeratinized epithelium, as well as nonkeratinized epithelium cover individual areas of the tongue. The rostral and caudal lingual glands present in the lamina propria of the body, lingual prominence and root of the tongue produce mucus. The specific arrangement of Grandry and Herbst corpuscles form so-called bill-tongue organ monitoring food transportation. Our research confirm that the lingual mucosa in domestic duck is characterized by microstructural species-specific modifications of particular areas of the tongue, which is formed not only under the influence of the filtering mechanism, but also by terrestrial feeding mechanisms such as grazing or pecking.

Function-related morphological characteristics and specialized structures of the avian tongue

As a reflection of different life styles and environment, the tongue of vertebrates, which plays a major role in the intake and swallowing of food, displays significant morphological differences. The gross form and microscopic structure of the avian tongue differ greatly according to lifestyle. The avian tongue plays a fundamental role in many functions such as capturing, filtering, sucking and manipulating food in order to compensate absence of subsidiary organs like teeth in the oropharyngeal cavity. Variations in lingual papillae play an important role in feeding of birds, as they represent a structure similar to teeth in the upper and lower beaks and can be used to hold and direct food in the oropharyngeal cavity. Tongues of birds exhibit common as well as varying anatomical characteristics in terms of surface morphology, structure and topographical distribution of lingual papillae as well as distinct specialized structures, epithelial layers, taste buds and lingual glands. This review evaluates the important morphological peculiarities of the tongue in birds, focusing on the relationship between anatomical features and feeding functions.

Histomorphological and Histochemical Observations of the Common Myna (Acridotheres tristis) Tongue

Common myna tongue was studied histomorphologically and histochemically. Four tongues of adult birds were carried out macroscopically and microscopically. The tongue was triangular; the dorsum of the body had median groove. Two to three backward directed papillae were located on each side of the body-base junction. A single transverse row of pharyngeal papillae was located behind the laryngeal cleft. The parakeratinized mucosa covered the entire surface of the tongue except clearly keratinized band on the ventrolateral surface and the conical papillae. Compared with the lateral group (LG), the secretory cells of the medial group (MG) of the anterior lingual glands (ALG) and the posterior lingual glands (PLG) contained large amount of mucin. It was neutral mucin. However, the LG had weak acid mucin with carboxylated group. Meanwhile, the MG of the ALG and the PLG had strong acid mucin with both carboxylated and sulphated groups. In conclusion, the morphological observation of the common myna tongue showed some variation from the other birds. Histochemical results indicated the differences between the LG and MG of the anterior lingual glands. However, no difference was observed between the latter and the PLG.

Anatomical and scanning electron microscopic investigations of the tongue and laryngeal entrance in the long-legged buzzard (Buteo rufinus, Cretzschmar, 1829)

This research aimed to examine the morphological features of the tongue and laryngeal entrance of long-legged buzzard by macroscopic and scanning electron microscopic methods. Two adult buzzards were used as material. The tongue was fairly elongated and terminated in oval shovel-like apex. Scale-like projections were localized on the apex and body of tongue. Both lateral sides of lingual body were contained considerably long thread-like projections. Many orifices of lingual posterior salivary glands were discerned among scale-like projections in median sulcus of the lingual body. Papillary crest of sharp conical papilla were observed on the between the body and root of the tongue. No conical papillae or other projections were existent on the root of the tongue, but numerous orifices of posterior salivary gland ducts were detected. In addition, orifices of anterior salivary gland ducts were present on the dorsal and lateral surfaces of the lingual body. Numerous conical papillae were observed on the caudal region of glottis and no conical papillae or any similar projection which were bordered the glottic fissure was noted. Anatomy of these organs in the long-legged buzzard and white tailed eagle which are the member of the same family, Accipitridae, revealed very high similarity.

Scanning electron microscopic study on the tongue in the scarlet macaw (Ara macao)

The dorsal lingual surface of scarlet macaw (Ara macao) was examined by scanning electron microscopy. Macroscopically, the lingual apex of the scarlet macaw had a lip-like shape. Three parts were distinguished in the dorsal surface of the tongue: the apex, body, and root of the tongue. The surface of the lingual apex had many grooves toward lingual root. The surface of the lingual apex was relatively smooth. The central surface of the papillary layer in the lingual apex after removal of the epithelium consisted of numerous dermal papillae, but the papillae were not observed in the lateral region. A pair of openings of the lingual glands was observed in the posterolateral region of the lingual body. The opening of the lingual gland after removal of the epithelium showed more clear structure than before removal. Many conical papillae in the posterior region of the lingual body were observed. The structure of the tongue of the scarlet macaw was different from that of the rainbow lorikeet.

Gross anatomical and scanning electron microscopic studies of the oropharyngeal cavity in the European magpie (Pica pica) and the common raven (Corvus corax)

There is no descriptive information about morphology of the oropharyngeal cavity including tongue, palate, and laryngeal region in Corvidae family. This study not only presents the first definitive anatomical description of the structures in the oropharyngeal cavity of magpie and raven but also reviews and compares the scattered information on the morphology of the other avian species available in the literature. In this study, the organs of four birds (two magpies and two ravens) were used. The tongue in magpie and raven was considerably elongated and terminated with an oval-shaped apex. Although the lingual apex in the magpie was divided by fissure, no such bifurcation existed on that of raven. Lingual apex was quite distinctive in both species, and multiple acicular processes covered the apex. These occurrences on the tongue of magpie were replaced by thread-like processes as approaching the lingual body. In raven, these processes were mostly foliated, becoming longer toward the back of the lingua, and denser compared with raven. Moreover, we observed conical papillary crest, which was pointed backward and located between the lingual body and the radix of the tongue and pharyngeal conical papillae around the glottis and palate clefts in both species. There was a transversal fold separating the choanal cleft from the infundibular cleft in raven. Anatomy of the oropharyngeal cavity in the raven and magpie, which are the member of the same family, Corvidae, showed little differences and overall their oral morphological features were excessively similar.

Functional morphology of the tongue in the domestic goose (Anser anser f. domestica)

Using LM and SEM methods, the study describes microstructures in particular areas of the tongue of the goose. A thick multilayered keratinized epithelium forms the "lingual nail" and covers small and giant conical papillae, whereby the first functions as an exoskeleton of the tongue apex, and the latter are arranged along the lingual and well-developed connective tissue cores, and together with the bill lamellae are involved in cutting. The row of conical papillae on the lingual prominence prevents regurgitation of transported food. In the area of the "lingual nail" and in the anterior part of the lingual prominence, Herbst corpuscles are accumulated, which allow to recognize food position. Filiform papillae, as widely distributed between the conical papillae of the body, are responsible for filtering. They can be explained as long keratinized processes of the epithelium and are devoid of connective tissue cores. During food transport, the flattened areas of the lingual body and the lingual prominence are protected by a parakeratinized epithelium, but the root is covered by a nonkeratinized epithelium. The presence of adipose tissue in the tongue probably reduces pressure during food passage, but also promotes mucus evacuation from the lingual glands, thus facilitating food transport. An entoglossal bone with a continuation as cartilage is the stable structural basis of the tongue system.

Gross anatomical features of the oropharyngeal cavity of the ostrich (Struthio camelus)

Most descriptions of the ostrich oropharynx and oesophagus are superficial and supply little meaningful morphological data. The aim of this investigation is describe the ostrich oropharingeal cavity, in order to supply the deficiency of macroscopic data about this important animal. Five heads of 12 to 14-month-old ostriches of either sex were anatomically dissected to expose the oropharynx. The ostrich oropharynx was "bell-shaped" composed by the maxillary and mandibular ramphoteca. The roof and floor presented two distinct regions different in colour of the mucosa. The rostral region was pale pink contrasting to creamy-pink coloured caudal region. The median longitudinal ridge extended rostrally from the apex of the choana to the tip of the beak in the roof and it is clearly more prominent and rigid than the homolog in the floor that appeared thin and stretched rostrally, continuing caudally surrounding the tongue and the laryngeal mound eventually merging with the oesophageal mucosa. The floor was formed by the interramal region, tongue and laryngeal mound containing shield-shaped glottis. It can be concluded that the present study, in addition to confirming the basic features of the oropharynx previously described for the ostrich, clarified the contradictory information presented in the literature and also provided new, unreported morphological data, some of which may be important when studying nutrition and health in these birds.