Morphological and Imaging Characterization of the Eye and Adnexa of the Lesser Anteater (Tamandua tetradactyla).

Abstract

The southern tamandua (Tamandua tetradactyla) is a species vulnerable to environmental disturbances, largely due to increasing overlap between its natural habitat and anthropogenically modified landscapes. Detailed anatomical knowledge of the eye and orbital structures, supported by imaging and histological analyses, is essential to improve clinical, surgical and conservation practices for wild mammals. This study provides a comprehensive anatomical description of the eyeball and its adnexa in the southern tamandua. Twelve cadaveric specimens were examined using topographic dissection, orbital exenteration, bone maceration, ocular ultrasonography, computed tomography and histological processing. The orbit was incomplete and shallow, formed by the frontal, lacrimal, parietal, temporal and sphenoid bones, and exhibited a pronounced lateral projection of the eye. The eyeball was relatively small in proportion to the skull, globoid in shape, slightly elongated along the anteroposterior axis, and characterized by a high corneoscleral ratio. The eyelids were well developed, bearing eyelashes on both margins. The third eyelid was triangular and supported by hyaline cartilage. The lacrimal gland was reduced in size, whereas the Harderian gland was voluminous, lobulated and ring-shaped, extensively surrounding the eye and occupying a substantial portion of the orbital cavity. Distinctive features of the extraocular musculature included duplication of the dorsal rectus muscle and absence of the dorsal oblique muscle. Ultrasonography enabled visualization of intraocular structures, and computed tomography confirmed orbital dimensions. Histological analysis revealed tissue organization consistent with the general mammalian pattern, with no evidence of a tapetum lucidum. These findings expand anatomical knowledge of Xenarthra and provide relevant reference data for veterinary ophthalmology, comparative anatomy and surgery, and the conservation of wild mammals.