Comparative Distribution and Arrangement of Herbst Corpuscles in the Oropharynx of the Ostrich (Struthio camelus) and Emu (Dromaius novaehollandiae)

Abstract

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.

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

“…The Herbst and Grandry corpuscles are found in both the beak and oral cavity in the domestic duck; however, mainly they are distributed in the caudal part of the beak (Leitner and Roumy 1974). The emu and ostrich are equipped only with the Herbst corpuscles (Crole and Soley 2014). Researchers have determined that skin mechanoreceptors in the rostral part of the beak and in the oral cavity form the so-called bill tip organ (Gottschaldt and Lausmann 1974; Berkhoudt 1980; Gentle and Breward 1986; Halata and Grim 1993).…”

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

“…Functionally, it may represent a structure that plays a role in absorbing mechanical energy produced by pecking against hard substrates (Crole & Soley, 2016). Meckel's cartilage would possibly prevent nerve fibres within the N. intramandibularis (Crole & Soley, 2016) from creating action potentials by direct mechanical stimulation as opposed to transporting action potentials initiated by mechanoreceptors in the bill tip (Crole & Soley, 2014). Gussekloo and Bout (2005) demonstrated that the forces experienced by the bill tip of the greater rhea during pecking were not great and were sufficiently spread over the bony surface area of the bill tip.…”

“…More recently, the bill tip of ratite species has received particular attention, initially in the Apterygidae where a bill tip organ was described in five extant kiwi species (Cunningham et al, 2013;Cunningham, Castro, & Alley, 2007). Subsequently, aspects of the rostral bill tips have been studied in the ostrich (Struthio camelus) and emu (Dromaius novaehollandiae) with regards to the bony bill tip (Crole & Soley, 2017), the branches of the trigeminal nerve supplying this region (Crole & Soley, 2016) and the distribution (Crole & Soley, 2014) and structure (Crole, du Plessis, & Soley, 2015) of Herbst corpuscles.…”

Size and number of the hypoglossal nerve foramina in the avian skull and their potential neuroanatomical significance

“…Because the hypoglossal nerve innervates both the tongue and the syrinx, it is finally noted that the evolution of the basicranial nerve foramina may also have been correlated with an increased importance of the tongue in feeding biology. This is possibly indicated by the separation of the foramina nervi vagi et glossopharyngealis in Neognathae, which exit through a single foramen in Enaliornis (Elzanowski & Galton, ) and in Palaeognathae, in which the tongue is rudimentary and exhibits different sensory properties than that of neognathous birds (Crole & Soley, ). Recently, it was furthermore hypothesized that a syrinx evolved late in avian evolution, in the lineage leading to modern birds (Clarke et al, ), and future studies will have to assess whether a refinement of the vocal system accounts for the derived features of the hypoglossus and glossopharyngeus nerves of neognathous birds.…”