Anatomy description of cervical region and hyoid apparatus in living giant anteaters Myrmecophaga tridactyla Linnaeus, 1758

Abstract

RESUMO.-[Descrição anatômica da região cervical e aparato hioide em espécimes vivos de tamanduá--bandeira, Mymercophaga tridactyla Linnaeus, 1758.] O Tamanduá-Bandeira possui adaptações anatômicas específicas, devido aos hábitos alimentares de ingestão de formigas e cupins. O arranjo singular do aparato hioide dos tamanduás é fundamental para a ingestão de alimentos. Sua descrição na literatura é baseada em peças e fósseis, o que dificulta a determinação de detalhes anatômicos existentes em animais vivos. As técnicas de imagem permitem a avaliação da anatomia topográfica dos animais, de maneira não invasiva, e o conhecimento desta é fundamental para o diagnóstico e prognóstico de afecções. O objetivo desse The giant anteater has specific anatomical adaptations resulting from its ant and termite feeding habits. The unique arrangement of its hyoid apparatus is essential for the ingestion of food. However, its description in the literature is based on fragments and fossils, making it difficult to determine existing anatomical details in live animals. Imaging techniques, which enable the topographical anatomy of animals to be examined noninvasively, provide essential information for the diagnosis and prognosis of diseases. The aim of this study is to describe the bone contours in the hyoid apparatus of the giant anteater by means of radiographic and tomographic images. Giant anteaters of varying ages from the Wild Animal Screening Center (CETAS-GO) were used, seven for X-ray exams and two adults for CT exams. The hyoid elements in all the animals were evaluated using the two imaging techniques, and were visualized in the cervical region of C2 to C6, which comprises three paired bones (stylohyoid, epihyoid, ceratohyoid) and one unpaired bone (basihyoid). The presence of air in the oropharynx enabled the assessment of soft tissue structures in this region, such as the epiglottis and the soft palate. CT axial sections are of limited usefulness for evaluating the hyoid bones, but enable assessments of the basihyoid bone and its characteristic V-shape. Thus, to analyze the hyoid region in anteaters based on radiographic and tomographic images, one must keep in mind that the stylohyoid, epihyoid and ceratohyoid bones are situated ventrally to the C2 to C5 vertebrae and that the basihyoid at the level of C5-C6 demarcates the transition between the nasopharynx and the trachea. The nasopharynx and oropharynx extend from C1 to C5, and the trachea begins at the level of C6.INDEX TERMS: Cervical region, hyoid apparatus, giant anteater, Myrmecophaga tridactyla, oropharynx, radiology, topographical anatomy, trachea, V-shaped bone, xenarthra.

Computed tomography and cross‐sectional anatomy of the head in the giant anteater (Myrmecophaga tridactyla)

“…The giant anteaters of this study presented the soft palate and the nasal and oral parts of the pharynx extended to the caudal level of the cervical region. These features were previously described in a study about cervical region and hyoid apparatus in living giant anteaters (Borges et al, 2017). The nasal and oral parts of the pharynx extended until the transition between the fifth and sixth cervical vertebrae, with the laryngeal part of the pharynx starting at this level (Borges et al, 2017).…”

“…This is more of an anatomical adaptation to accommodate the elongated tongue (Reiss, 1997;Naples, 1999;Borges et al, 2017). Borges et al, (2017) reported that it is important to know these anatomical details to avoid incorrectly identifying the nasal part of the pharynx as the cervical part of the trachea.…”

“…The ability to retract the elongated tongue is supported by the also elongated hyoid apparatus, in particular by the stylohyoid bones (Naples, 1999). The cranial portion of the stylohyoid bone presented no correlation to the bony structures of the skull (Borges et al., 2017). The stylohyoid bones were visible in the tomographic and anatomical images of this study.…”

“…The giant anteater ( Myrmecophaga tridactyla ) is the largest representative of the Myrmecophagidae family (Borges et al., 2017), with wide geographic distribution and that appears in all Brazilian biomes, from the Amazon to the southern fields (Miranda, 2012). Besides that, it is the largest species among neotropical vermilinguans (Gaudin et al., 2018).…”

“…The knowledge of anatomy is extremely important for the diagnosis and prognosis of wild animals, with imaging diagnostic being an important tool in diagnosis and treatment since it allows observing the topography of animals in a non‐invasive way (Borges et al., 2017; Cunha et al., 2018; Costa et al., 2019). The computed tomography (CT) is adequate to measure, study and distinguish different types of tissues and structures, in addition to providing more accurate diagnoses in a shorter time.…”