Fine structure of the dorsal lingual epithelium of the little tern, Sterna albifrons Pallas (Aves, Lari)

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.

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.

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.

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.

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.

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.

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.

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.

Gross anatomical features of the gastrointestinal tract (GIT) of blue and yellow macaws (Ara ararauna) - oral cavity and pharynx

Morphological studies of the gastrointestinal tract (GIT) of blue and yellow macaws (Ara ararauna) are scarce. Therefore, this study aims to describe the macaw's oropharyngeal cavity in order to supply the deficiency of anatomical data and as part of a broad study of the GIT of these birds. Two male and one female adult blue and yellow macaws were anatomically dissected to expose the oropharynx. The macaw oropharynx was 'V-shaped' and flattened laterally being composed of maxillary and mandibular rhamphotheca of the beak. The tongue, lingual frenulum and laryngeal mound (containing 'spindle-shaped' glottis and prominent mucosal papillae) formed the floor of the oropharynx. The roof revealed two distinct regions separated by a 'step-like depression', whereas in the floor, the mandibular rhamphotheca was separated from the oral cavity mucosa by a large vestibulum enclosing the lingual frenulum. The palate was hard without any signs of rugae nor palatine raphe. A smooth ridge extended caudally from the choana to the common opening of the Eustachian tubes. This study, in addition to confirming the basic features of the oropharynx previously described for birds in general, provided new, unreported morphological data, some of which may be important when studying nutrition and health of these birds.

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.

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 nutcracker (Nucifraga caryocatactes)

The nutcracker Nucifraga caryocatactes belongs to a group of bird species that use their beak and tongue as tools for obtaining food, such as seeds from hard-to-reach cones or nuts from shells. The aim of the present study, carried out with a scanning electron microscope, was to define the morphological features of the tongue of the nutcracker, which seems to be adapted to its environment through specific methods of obtaining food. One of the characteristic features of the nutcracker's tongue is the unique structure of the anterior part of the tongue, which has two long and highly keratinized processes - a product of the renewable keratinized layer of the epithelium covering the ventral surface of the tongue. These dagger-like processes, which are a modified "lingual nail," take a major role in levering up and shelling seeds, which are transported over the short sulcus-shaped body of the tongue. A unique feature of the nutcracker's tongue is the groove separating the body from the root. Two rows of highly keratinized, mechanical, conical papillae are located at the junction of the body and the root. These papillae are mechanically protective elements for passing food particles in the form of seeds. Among lingual glands, only the posterior lingual glands on the root of the tongue have been observed. Their secretion agglutinates dry food before it is swallowed. Results of the present study indicate that the nutcracker's tongue is an efficient tool resembling a lever that is helpful in shelling seeds.

Surface morphology of the emu (Dromaius novaehollandiae) tongue

Despite numerous morphological studies on the avian tongue, very little meaningful information is currently available on the surface features of this organ using scanning electron microscopy (SEM). The only SEM description of a ratite tongue is that of the ostrich, although the descriptions are brief and superficial. This SEM study of the emu tongue confirms and compliments the comprehensive macroscopic and histological data available for this commercially important species. The tongues of five emus were fixed, cut into blocks representing the dorsum, ventrum and root and routinely processed for SEM. Three morphologically distinguishable surface types (desquamating, non-desquamating and lymphoepithelium) related to peculiarities in surface cell shape and status (desquamating or non-desquamating), cell surface modifications and distribution of gland openings, and which showed a regional distribution, could be identified. Three basic types of cell surface modifications (microplicae, microvilli and cilia) were observed, with microvilli and cilia being described for the first time in an avian tongue by SEM. The desquamating surface cells fulfil a mechanical protective function, whereas the microplicae, microvilli and cilia appear to be adaptations for the trapping and spreading of mucus which also fulfils a protective function.

Light and scanning electron microscopic study of the structure of the ostrich (Strutio camelus) tongue

The ostrich's tongue is situated in the posterior part of the oropharyngeal cavity and its length is only about a quarter of the beak cavity. The triangular shortened tongue has retained the usual division into the apex, the body and the root. There are no conical papillae between the body and the root of the tongue, and the presence of the flat fold with lateral processes sliding over the tongue root in the posterior part of the lingual body is a unique morphological feature. All lingual mucosa covers non-keratinised stratified epithelium, and the lamina propria of the mucosa is filled with mucous glands whose round or semilunar openings are found on both the dorsal and ventral surface of the tongue. The complex glands found in the lingual body are composed of alveoli and/or tubules. Moreover, simple tubular glands seen in the posterior part of the tongue root are an exception. Numerous observations have shown that the ostrich's tongue is a modified structure, though not a rudimentary one, whose main function is to produce the secretion moisturising the beak cavity surface and the ingested semidry plant food in this savannah species.

Light and scanning electron microscopic study of the tongue in the cormorant Phalacrocorax carbo (Phalacrocoracidae, Aves)

The tongue of the cormorant Phalacrocorax carbo is a small, immobile structure with a length of 1.4 cm, situated in the middle part of the elongated lower bill. The uniquely shaped tongue resembles a mushroom, with a short base and an elongated dorsal part with sharpened anterior and posterior tips. A median crest can be observed on the surface of the tongue. Examination by light and scanning electron microscopy revealed that the whole tongue is formed by a dense connective tissue with many bundles of elastic fibers. The lingual mucosa is covered by a multilayered keratinized epithelium. The thickest, horny layer of the lingual epithelium was observed on the surface of the median crest and on the posterior tip of the tongue. Lingual glands are absent in cormorants. The framework of the tongue is composed of a hyoid cartilage incorporated into the base. The localization and structure of the tongue in the cormorant show that it is a rudimentary organ and that the lingual body, usually well-developed in birds, is conserved.

Evolution of the structure and function of the vertebrate tongue

Studies of the comparative morphology of the tongues of living vertebrates have revealed how variations in the morphology and function of the organ might be related to evolutional events. The tongue, which plays a very important role in food intake by vertebrates, exhibits significant morphological variations that appear to represent adaptation to the current environmental conditions of each respective habitat. This review examines the fundamental importance of morphology in the evolution of the vertebrate tongue, focusing on the origin of the tongue and on the relationship between morphology and environmental conditions. Tongues of various extant vertebrates, including those of amphibians, reptiles, birds and mammals, were analysed in terms of gross anatomy and microanatomy by light microscopy and by scanning and transmission electron microscopy. Comparisons of tongue morphology revealed a relationship between changes in the appearance of the tongue and changes in habitat, from a freshwater environment to a terrestrial environment, as well as a relationship between the extent of keratinization of the lingual epithelium and the transition from a moist or wet environment to a dry environment. The lingual epithelium of amphibians is devoid of keratinization while that of reptilians is keratinized to different extents. Reptiles live in a variety of habitats, from seawater to regions of high temperature and very high or very low humidity. Keratinization of the lingual epithelium is considered to have been acquired concomitantly with the evolution of amniotes. The variations in the extent of keratinization of the lingual epithelium, which is observed between various amniotes, appear to be secondary, reflecting the environmental conditions of different species.

Ultrastructural study of the relationship between the morphogenesis of filiform papillae and the keratinisation of the lingual epithelium in the rat

Tongues were removed from rat fetuses on d 16 of gestation (E16) and from newborn (P0) and juvenile rats on d 7 (P7) and d 21 (P21) postnatally for examination by light and transmission electron microscopy. In the fetuses at E16, no rudiments of filiform papillae were visible on the dorsal surface of the tongue. No evidence of keratinisation could be recognised over the entire dorsal lingual epithelium. At P0, rudiments of filiform papillae showed a similar distribution to that seen in the adult, but had a more rounded appearance. The columnar structure of cells in the epithelium, with the different degrees of keratinisation as observed in the mature adult, was indistinct, but a keratinised layer was clearly located at the tip of each filiform papilla. In juveniles at P7, the filiform papillae on the anterior part of the tongue were long and slender, and the anterior and posterior cell columns of the filiform papillae and the interpapillary cell columns were clearly distinguishable. In juveniles at P21, the structure of filiform papillae was identical to that in the adult. These results indicate that, in rats, the morphogenesis of filiform papillae advances in parallel with keratinisation of the lingual epithelium from just before birth to a few weeks after birth.

Ultrastructural study of the keratinization of the dorsal epithelium of the tongue of Middendorff's bean goose, Anser fabalis middendorffii (Anseres, Antidae)

BACKGROUND

Comparative studies of ultrastructural features of tongues allow deductions to be made about relationships between structure and function, as reflected by an animal's feeding habits. The present study was performed to serve as a basis for further studies of avian feeding mechanisms and of relationships between the fine structure of the lingual epithelium and the development of the expression of keratins.

METHODS

The light microscope, scanning electron microscope, and transmission electron microscope were used.

RESULTS

The dorsal surface of the tongue of Middendorff's bean goose, Anser fabalis middendorffii, has a distinctive anterior region that extends for five-sixths of its length and has a clear posterior region. The anterior region, when observed macroscopically and by scanning electron microscopy, is distinguished along its forward half by a clear median line. The back half of the anterior region has an indistinct median sulcus in some parts. There are no lingual papillae on the entire dorsal surface of the anterior and posterior regions. Giant conical papillae are located in a transverse row between the anterior and posterior regions. On both lateral sides of the anterior region for five-sixths of the length of the tongue, lingual hairs are compactly distributed, and small numbers of large cylindrical papillae are arranged at almost regular intervals between these lingual hairs. Examination of the dorsal lingual epithelium by light and transmission electron microscopy provided histological and cytological criteria for distinguishing the anterior and posterior regions, both of which were composed of stratified squamous epithelium. Basal cells were similar throughout the dorsal epithelium. The intermediate layer of cells in the anterior region contained numerous tonofibrils in electron-dense bundles composed of tonofilaments of 10 nm in diameter. The outer layer was composed of electron-dense, well-keratinized cells, with layers of electron-lucent cells on the outermost surface. The cells in the intermediate layer in the posterior region of the tongue were almost completely filled with unbundled tonofilaments. The surface layer exhibited features of parakeratinization. In all of the giant conical papillae, the large cylindrical papillae, and the lingual hairs, the epithelium was strongly keratinized.

CONCLUSIONS

The three-dimensional microanatomy and cytological features of the dorsal lingual epithelium of avians seem to be related to the functional role and shape of the tongue of each species in feeding.

Dorsal lingual epithelium of Platemys pallidipectoris (Pleurodira, Chelidae)

Scanning electron microscopy reveals that the flat tongue of Platemys pallidipectoris has shallow grooves and no lingual papillae. The surface of the tongue is covered with dome-shaped bulges, each corresponding to a single cell. Short microvilli are distributed over the cell surface. Light microscopy shows a stratified cuboidal epithelium with an underlying strong connective tissue. Transmission electron microscopy indicates four layers. The basal cells of the epithelium are electron-translucent and have a large central nucleus and a cytoplasm with keratin tonofilaments. Plasma cells with abundant rough endoplasmic reticulum and mitochondria occur in the basal layer. Production of secretory granules begins in the more electron-dense intermediate layers and increases as the cells move toward the surface. The membranes of the cells of the deep intermediate layer form processes that project into relatively wide intercellular spaces. In the superficial intermediate layer, the cytoplasm of the cells contains numerous fine granules; these increase in number but not in size in more distal layers. The cells of the surface layer are electron-translucent with a round nucleus. Contents of their fine granules are secreted into the oral cavity. © 1995 Wiley-Liss, Inc.