A gross anatomical and histological study of the oropharynx and proximal oesophagus of the emu (Dromaius novaehollandiae)

This study describes the gross anatomical, histological and surface morphological features of the oropharynx and proximal oesophagus of the emu in order to address the scarcity of information on this region in this commercially important bird. Heads obtained from birds at slaughter (and a younger and older bird from emergency farm slaughter) were used for this study and described using basic gross anatomical and histological techniques, supplemented by scanning electron microscopy. The findings of the study were compared with the relevant literature. The oral and pharyngeal cavities could not be morphologically separated and formed a single cavity. This cavity was dorso-ventrally flattened and clearly divided, both on the floor and the roof, into rostral pigmented and caudal non-pigmented parts. The non-pigmented floor housed the tongue and laryngeal mound which had a wide glottis and no papillae. The choana was triangular-shaped, with a small caudo-lateral fold on either side, and was situated in the nonpigmented part of the roof. Caudal to the choana were two rounded pharyngeal folds with a pitted ventral surface. A small bilateral projection from the caudo-lateral edge consisted mainly of diffuse lymphoid tissue. The pharyngeal folds contained numerous large simple branched tubular mucus-secreting glands as well as large accumulations of lymphoid tissue. The pigmented regions of the roof and floor were aglandular and lined by a keratinised stratified squamous epithelium which, particularly in the roof, contained numerous Herbst corpuscles in the underlying connective tissue. SEM revealed the surface to be composed of sheets of desquamating flattened polygonal cells. The non-pigmented regions were glandular and lined by a non-keratinised stratified squamous epithelium. Surface cells displayed a pattern of microplicae or microvilli while individual surface cells were seen to desquamate. The connective tissue housed small, simple tubular and large, simple branched tubular mucus-secreting glands, Herbst corpuscles (only absent from the pharyngeal folds and proximal oesophagus), lymphoid tissue, blood vessels and nerves. The glands of the upper digestive tract were polystomatic and named as follows according to their location: Caudal intermandibular, lingual, crico-arytenoid, oral angular, caudal palatine, pharyngeal and oesophageal. The openings of the glands to the surface were seen on SEM as variably sized holes on the surface, some being obscured by mucus secretions from the underlying glands. Taste receptors were sparse and present only in the caudal non-pigmented oropharyngeal floor, tongue root and proximal oesophagus. Accumulations of lymphoid tissue were identified at the junction between the two regions of the roof, and in the non-pigmented roof, the non-pigmented floor, tongue ventrum, root and frenulum, proximal oesophagus and pharyngeal folds. The consistent dense accumulation of lymphoid tissue in the pharyngeal folds constituted pharyngeal tonsils (Lymphonoduli pharyngeales). The lymphoid tissue of the non-pigmented floor was visible macroscopically as round raised nodules. Specific, unnamed larger lymphoid tissue aggregations were located at the junction of the tongue ventrum and frenulum and in the small folds lateral to the choana. Surface morphology, as seen by SEM, revealed a pattern of microridges on the surface cells of the keratinised areas, whereas the surface cells of the non-keratinised areas displayed microplicae, microvilli and cilia. Microvilli and cilia were associated with the gland openings and ducts. The proximal oesophagus was a cylindrical tube with a longitudinally folded mucosa and displayed the typical tissue layers described in birds. The mucosa was formed by a nonkeratinised stratified epithelium which on SEM showed minimal surface desquamation. The lamina propria contained numerous simple tubular mucus-secreting glands which sometimes branched and occasional diffuse lymphoid tissue aggregations. The gland openings to the surface were seen on SEM as small and large dark holes. The muscularis mucosae was very prominent and was a longitudinal smooth muscle layer separating the mucosa from the submucosa. The tunica muscularis was composed of a thicker inner circular and a thinner outer longitudinal smooth muscle layer surrounded by the outer loose connective tissue forming the tunica adventitia. The emu tongue was divided into a body and a root. The body was triangular, dorso-ventrally flattened, pigmented and displayed caudally directed lingual papillae on both the lateral and caudal margins. The root, a more conspicuous structure in comparison to other ratites, was triangular, with a raised bulbous component folding over the rostral part of the laryngeal fissure. The lingual skeleton was formed by the triangular-shaped paraglossum (hyaline cartilage), forming the core of the tongue body, and the rostral projection of the basihyale, ventral to the paraglossum. Following the general trend in ratites, the emu tongue was greatly reduced in comparison to the bill length and specifically adapted for swallowing during the cranioinertial method of feeding employed by palaeognaths. The tongue was invested by a non-keratinised stratified squamous epithelium. The glands in the connective tissue formed the bulk of the parenchyma and were composed of both small simple tubular and large simple branched tubular mucus-secreting glands similar to those seen in the oropharynx. The lingual glands were grouped as follows: dorsal and rostro-ventral (large glands), caudo-ventral and radical (large and small glands) and frenular (small glands). The large glands were visible macroscopically as doughnut-shaped structures. Melanocytes were absent from the tongue ventrum and occasionally from the tongue root. Lymphoid tissue was absent from the tongue dorsum. Herbst corpuscles were present in the tongue body and root and generally closely associated with the large mucus-secreting glands. The surface morphology varied in the different regions of the tongue. The dorsal and rostro-ventral tongue body showed individual desquamating cells and large gland openings only, the caudo-lateral ventrum showed less desquamation and both large and small openings. The mid-ventral aspect had an undulating uneven appearance with round raised cells on the surface which were densely packed with microvilli. Very large, large and small openings were present in this region and ciliated cells occurred in the vicinity of gland openings. This study presented various unique findings regarding the morphology of the emu oropharynx compared to other ratites. Although the sense of taste has been confirmed in many avian species, this study presented the first evidence of taste in the emu and ratites in general and suggests the possibility of taste being previously overlooked in the other birds studied (ostrich and greater rhea). The tongue root of the emu was clearly defined and is unique in structure and possible function amongst the ratites and other birds. Previously unmentioned functions of the emu tongue revealed by this study include: touch (Herbst corpuscles), taste (taste bud), lubrication and mechanical protection (mucus-secreting glands), immunological (lymphoid tissue) and digestive (swallowing). It was also noted that the various structures and organs of the oropharynx revealed important and often interesting differences between the emu and the other ratites documented. The prominent serrations of the rostral mandibular tomia of the emu also appear to be unique amongst ratites. The presence and wide distribution of Herbst corpuscles within the emu oropharynx and tongue show these areas to be highly sensitive to touch. The caudo-lateral projections of the pharyngeal folds effectively formed pharyngeal tonsils, a feature not apparent in other ratites. Despite the differences noted between the emu and other ratites it was possible to discern a common pattern of structures and features, with their modifications, both within and forming the oropharynx in this group of birds.Dissertation (MSc)--University of Pretoria, 2009.Anatomy and Physiologyunrestricte

Gross morphology of Musculi bulbi of the ostrich (Struthio camelus) and emu (Dromaius novaehollandiae)

The avian eye is uniquely adapted and reflects some structural peculiarities in comparison to mammals. M. bulbi consists of four rectus, two oblique and two nictitating membrane muscles. These have been described in several avian species, including the ostrich. The ostrich and emu are commercially important and a description of M. bulbi would aid in diagnostics and surgery. Three sub-adult ostrich and three sub-adult emu heads were collected after slaughter in a commercial abattoir and immersion fixed in 10% neutral-buffered formalin. Enucleation involved removing extra-ocular tissues and incising the origins of M. bulbi in half the specimens and the insertions in the remainder. M. bulbi was described and compared. In both species M. bulbi was composed of eight thin, sheetlike muscles; with the two nictitating membrane muscles being more robust. M. rectus dorsalis / ventralis / lateralis / medialis originated peripherally to the For. optici. M. obliquus dorsalis / ventralis originated dorsally and rostrally to those above. The straight and oblique muscles inserted near the equator. Minor differences in the attachments of these muscles were noted between the species. M. quadratus / pyramidalis membranae nictitantis originated dorsally and ventro-medially on the equator, respectively. The pyramidal muscle inserted on the nictitating membrane via a long tendon to which the quadrate muscle also attached. M. bulbi was similar in both species and the minor differences need to be morphometrically quantified. Functions of the muscles were comparable in both species. A similar surgical procedure for enucleation is recommended in the ostrich and emu.Poster presented at the University of Pretoria, Faculty of Veterinary Science Faculty Day, August 25, 2016, Pretoria, South Africa.ab201

Gross anatomical features of the tongue, lingual skeleton and laryngeal mound of Rhea americana (Palaeognathae, Aves) : morpho-functional considerations

The tongue body of Rhea americana is triangular and partially pigmented with each caudo-lateral margin displaying a round, sub-divided lingual papilla. The tongue root is a smooth, non-pigmented tract of mucosa. The tongue body is supported by the paraglossum and distal half of the rostral projection of the basihyal (RPB), and the tongue root by the proximal half of the RPB, body of the basihyal and proximal ceratobranchials. An urohyal is absent; however, peculiar to R. americana, the caudal margin of the cricoid body displays a median projection, which may represent the remnant of the urohyal incorporated into the cricoid. The laryngeal mound is less elevated, the arytenoid cartilages are smaller than in other ratites, and the caudal margin displays pharyngeal papillae that vary in shape and number. The unique morphology of the lingual skeleton and its positioning within the tongue of R. americana, the rostral insertion of the M. ceratoglossus, the absence of the urohyal (enhanced ventroflexion) and the caudal positioning and mobile attachment of the ensheathed basihyal to the paraglossum would appear to allow independent movement of the tongue body relative to the hyobranchial apparatus. Additionally, the deeply indented base and rostral oval opening in the paraglossum limits the length of cartilage present in the midline of the tongue body. This may allow the tongue the necessary flexibility for the lingual papillae to clean the choana. The cleaning action of the tongue would occur simultaneously with the previously described role of this organ and associated structures during feeding. Thus, the so-called reduced, ancestral tongue of R. americana may be structurally and functionally more complex than previously believed.The National Research Foundation (NRF) and the University of Pretoria, South Africa,http://http://www.springer.com/life+sciences/animal+sciences/journal/435ab201

Distribution and structure of glandular tissue in the oropharynx and proximal esophagus of the emu (Dromaius novaehollandiae)

The glandular regions of the upper digestive tract in the emu were non-pigmented (except for the tongue in most specimens) and invested by a non-keratinised stratified squamous epithelium. The glands found in these regions were exclusively simple in nature and composed of tubular secretory units lined by Periodic Acid Schiff Stain-positive mucus-secreting cells. The naming of the various glandular fields was based on previously identified anatomical features and on nomenclature modified from previous studies on birds. The glands were classified into two main types, namely, simple tubular and simple branched tubular mucus-secreting glands. Simple branched tubular glands were a feature of the regions exposed to the greatest amount of friction during feeding, whereas simple tubular glands were a feature of regions exposed to less friction. The saliva produced by the salivary glands in birds functions to moisturize and lubricate food boli. Mucins in saliva also protect mucosal surfaces from desiccation and mechanical damage, assist in maintaining cellular water balance, provide lubrication and have an antimicrobial action. This study suggests that, in addition to the role of specific gross anatomical features, the type and distribution of glandular tissue in the emu upper digestive tract supports the cranioinertial feeding method employed by this species.University of Pretoria, South Africa.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1463-6395ab201

Persistence of Meckel's cartilage in sub‐adult Struthio camelus and Dromaius novaehollandiae

This study describes the persistence of an embryonal structure through to sub‐adulthood in the ostrich and emu. Mandibles from sub‐adult ostrich and emu were subjected to special staining, light microscopy and dissected to reveal and describe Meckel's cartilage. Meckel's cartilage, composed of hyaline cartilage, was present within the neurovascular canal of both species. The persistence through to sub‐adulthood of Meckel's cartilage in the ostrich and emu is a feature not previously reported in any other avian species. The proximal end of Meckel's cartilage was ossified in the region of the articular bone and the distal end was ossified in some specimens. Although this structure may ossify at a much later stage in life, the function in young and sub‐adult birds may be to dampen shockwaves along the intramandibular nerve that result from the action of pecking. In the ostrich, the M. pseudotemporalis superficialis tendon inserted onto the supra‐angular bone and Meckel's cartilage. In the emu, a small portion of the tendon was attached to the supra‐angular bone and the main part to Meckel's cartilage. The persistence of Meckel's cartilage in adult lepidosaurs, crocodilians and ratites represents an unusual shared trait between the extant members of the above groups.The University of Pretoria and the National Research Foundation.http://wileyonlinelibrary.com/journal/azo2021-04-01hj2020Anatomy and Physiolog

Contrasting morphological evidence for the presence of taste buds in Dromaius novaehollandiae and Struthio camelus (Palaeognathae, Aves)

This study, facilitated by the use of immunohistochemistry, indicated the presence of taste buds in Dromaius novaehollandiae but not in Struthio camelus. Seen at the light microscope level, the taste buds consisted of follicular cells and receptor cells. The follicular cells were located at the periphery of the taste bud, essentially encapsulating the receptor cells. Two morphologically distinct receptor cells were identified. Immunohistochemical labelling for neurofilament identified gustatory nerves within the taste bud. The distribution of taste buds in D. novaehollandiae matched strategic locations in the oropharynx along which food could be sampled, according to the feeding method described for these birds. Future feeding studies would be necessary in D. novaehollandiae to determine the importance of taste discrimination in their diet. This study represents the first confirmed report of a sense of taste in any ratite species.University of Pretoriahttp://link.springer.com/journal/4352016-09-30hb201

Comparative distribution and arrangement of Herbst corpuscles in the oropharynx of the ostrich (Struthio camelus) and emu (Dromaius novaehollandiae)

Herbst corpuscles are widely distributed throughout the oropharynx of the ostrich and emu in contrast to the general situation in birds. Knowledge of the comparative distribution of Herbst corpuscles in the oropharynx of these two commercially important ratite species may assist in a better understanding of their feeding habits. Tissue sections representing all parts of the oropharynx of five ostrich and five emu heads collected after slaughter were prepared for light microscopy, the Herbst corpuscles counted, and the relative percentage of corpuscles calculated for defined anatomical regions. Herbst corpuscles were more widespread in the oropharynx of the emu (where they were additionally found in the tongue and laryngeal mound) than in the ostrich but were absent from the pharyngeal folds in both species. The results further indicated that Herbst corpuscles were strategically located to aid in the handling and transport of food. In this context, the high concentration of Herbst corpuscles in the prominent median palatine and ventral ridges in the ostrich denote these structures as sensory organs, namely the palatal and interramal organs. The presence of these sensory organs, coupled with the higher relative percentage of Herbst corpuscles located on the rostral oropharyngeal floor, indicate that the part of the oropharynx caudal to the mandibular and maxillary rostra forms an important sensory region in the ostrich. Additionally, speciesspecific concentrations of Herbst corpuscles within the oropharynx were identified which appear to assist in the accurate positioning of the tongue and laryngeal mound for cleaning the choana (internal nares) after swallowing.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1932-8494hb201

What prevents Struthio camelus and Dromaius novaehollandiae (Palaeognathae) from choking? A novel anatomical mechanism in ratites, the linguo-laryngeal apparatus

BACKGROUND: The avian glottis channels air from the oropharynx to the trachea and is situated on an elevated structure, the laryngeal mound. It is imperative that the glottis be protected and closed during swallowing, which in mammals is achieved by covering the glottis with the epiglottis, as well as by adduction of the arytenoid cartilages. An epiglottis, however, is reportedly absent in birds. Ratites such as Struthio camelus and Dromaius novaehollandiae possess a very wide glottis in comparison to other birds. The question therefore arises as to how these large birds avoid inhalation of ingesta through a wide glottis, with apparently little protection, particularly as their feeding method involves throwing the food over the glottis to land in the proximal esophagus. RESULTS: In S. camelus when the glottis was closed and the tongue body retracted, the smooth tongue root became highly folded and the rostral portion of the laryngeal mound was encased by the pocket in the base of the \ − shaped tongue body. In this position the lingual papillae also hooked over the most rostral laryngeal projections. However, in D. novaehollandiae, retraction of the tongue body over the closed glottis resulted in the prominent, triangular tongue root sliding over the rostral portion of the laryngeal mound. In both S. camelus and D. novaehollandiae these actions resulted in the rostral portion of the laryngeal mound and weakest point of the adducted glottis being enclosed and stabilised. CONCLUSIONS: Only after conducting a comparative study between these two birds using fresh specimens did it become clear how specific morphological peculiarities were perfectly specialised to assist in the closure and protection of the wide glottis. We identify, describe and propose a unique anatomical mechanism in ratites, which may functionally replace an epiglottis; the linguo-laryngeal apparatus.The University of Pretoria and the National Research Foundation (NRF) (J. Soley Incentive Funding Grant no. 73279).http://www.frontiersinzoology.com/content/9/1/11ab2012ab2013 (Author correction

Evidence of a true pharyngeal tonsil in birds : a novel lymphoid organ in Dromaius novaehollandiae and Struthio camelus (Palaeognathae)

BACKGROUND: Tonsils are secondary lymphoid organs located in the naso- and oropharynx of most mammalian species. Most tonsils are characterised by crypts surrounded by dense lymphoid tissue. However, tonsils without crypts have also been recognised. Gut-associated lymphoid tissue (GALT), although not well-organised and lacking tonsillar crypts, is abundant in the avian oropharynx and has been referred to as the “pharyngeal tonsil”. In this context the pharyngeal folds present in the oropharynx of ratites have erroneously been named the pharyngeal tonsils. This study distinguishes between the different types and arrangements of lymphoid tissue in the pharyngeal region of D. novaehollandiae and S. camelus and demonstrates that both species possess a true pharyngeal tonsil which fits the classical definition of tonsils in mammals. RESULTS: The pharyngeal tonsil (Tonsilla pharyngea) of D. novaehollandiae was located on the dorsal free surface of the pharyngeal folds and covered by a small caudo-lateral extension of the folds whereas in S. camelus the tonsil was similarly located on the dorsal surface of the pharyngeal folds but was positioned retropharyngeally and encapsulated by loose connective tissue. The pharyngeal tonsil in both species was composed of lymph nodules, inter-nodular lymphoid tissue, mucus glands, crypts and intervening connective tissue septa. In S. camelus a shallow tonsillar sinus was present. Aggregated lymph nodules and inter-nodular lymphoid tissue was associated with the mucus glands on the ventral surface of the pharyngeal folds in both species and represented the Lymphonoduli pharyngeales. Similar lymphoid tissue, but more densely packed and situated directly below the epithelium, was present on the dorsal, free surface of the pharyngeal folds and represented a small, non-follicular tonsil. CONCLUSIONS: The follicular pharyngeal tonsils in D. novaehollandiae and S. camelus are distinct from the pharyngeal folds in these species and perfectly fit the classical mammalian definition of pharyngeal tonsils. The presence of a true pharyngeal tonsil differentiates these two ratite species from other known avian species where similar structures have not been described. The pharyngeal tonsils in these ratites may pose a suitable and easily accessible site for immune response surveillance as indicated by swelling and inflammation of the tonsillar tissue and pharyngeal folds. This would be facilitated by the fact that the heads of these commercially slaughtered ratites are discarded, thus sampling at these sites would not result in financial losses.The University of Pretoria and the National Research Foundation (NRF) (JTS Incentive Funding Grant no. 73279)http://www.frontiersinzoology.com/content/9/1/21ab201

Gross morphology and topographical relationships of the hyobranchial apparatus and laryngeal cartilages in the ostrich (Struthio camelus)

The ostrich hyobranchial apparatus consists of the centrally positioned paraglossalia and basiurohyale and paired caudo-lateral elements (horns), each consisting of the ceratobranchiale and epibranchiale. The paraglossalia lie within the tongue parenchyma and consist of paired, flat, caudo-laterally directed cartilages joined rostrally. The basiurohyale forms a single dorso-ventrally flattened unit composed of an octagonal-shaped body from which extend rostral (the rostral process) and caudal (the urohyale) projections. The laryngeal skeleton consists of cricoid, procricoid and paired arytenoid cartilages. The large ring-shaped cricoid cartilage displays a body and paired wings which articulate with each other and with the procricoid. The blunt, ossified, rostral projection of the cricoid and the scalloped nature of the arytenoid cartilages are unique to the ostrich. The procricoid is a single structure which links the paired arytenoids and wings of the cricoid. The hyobranchial apparatus is firmly attached to the tongue parenchyma and to the larynx and proximal trachea. In contrast to previous reports in this species, the horns of the hyobranchial apparatus are not related to the skull. Ossification of the body of the basihyale, the ceratobranchials and the rostral process and body of the cricoid cartilage of the larynx lends stability to these structures.University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1463-63952016-10-31hb2016Anatomy and Physiolog