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

Abstract

The giant anteater has specific anatomical adaptations resulting from its ant and termitefeeding habits. The unique arrangement of its hyoid apparatus is essential for the ingestionof food. However, its description in the literature is based on fragments and fossils, makingit difficult to determine existing anatomical details in live animals. Imaging techniques,which enable the topographical anatomy of animals to be examined noninvasively, provideessential information for the diagnosis and prognosis of diseases. The aim of this studyis to describe the bone contours in the hyoid apparatus of the giant anteater by meansof radiographic and tomographic images. Giant anteaters of varying ages from the WildAnimal Screening Center (CETAS-GO) were used, seven for X-ray exams and two adults forCT exams. The hyoid elements in all the animals were evaluated using the two imagingtechniques, and were visualized in the cervical region of C2 to C6, which comprises threepaired bones (stylohyoid, epihyoid, ceratohyoid) and one unpaired bone (basihyoid). Thepresence of air in the oropharynx enabled the assessment of soft tissue structures in thisregion, such as the epiglottis and the soft palate. CT axial sections are of limited usefulnessfor evaluating the hyoid bones, but enable assessments of the basihyoid bone and its characteristicV-shape. Thus, to analyze the hyoid region in anteaters based on radiographic andtomographic images, one must keep in mind that the stylohyoid, epihyoid and ceratohyoidbones are situated ventrally to the C2 to C5 vertebrae and that the basihyoid at the level ofC5-C6 demarcates the transition between the nasopharynx and the trachea. The nasopharynxand oropharynx extend from C1 to C5, and the trachea begins at the level of C6.