ABSTRACT
Tamandua mexicana is an anteater species native from Mexico to Peru. This species is of great evolutionary interest because it belongs to one of the oldest clades of placental mammals in the American continent. This study aimed to describe the origin, insertion, and arterial supply of the intrinsic shoulder and brachial muscles of T. mexicana. We also compared the masses of the functional groups. Gross dissections were performed on both thoracic limbs of 13 cadavers. ANOVA followed by Tukey's test was used for statistical analyses. The subscapularis muscle presents a hiatus to the common tendon of the caput breve of the biceps brachii and coracobrachialis muscles. A variant accessory muscle, the m. articularis humeri lateralis, was found on the lateral surface of the shoulder joint. M. deltoideus pars acromialis has two bellies. The teres major muscle is perforated by the aponeurotic origin of the m. tensor fasciae antebrachii. The triceps brachii has two capita longi. The caput mediale is fused with the m. anconeus medialis. The caput laterale can have an accessory belly as an anatomical variant. Among the functional groups, a significant difference was found between the elbow extensors and flexors, with the latter having the lowest mass. In conclusion, the intrinsic muscles of T. mexicana presented unique features for the species, as well as arrangements in mass distribution that evidence a possible evolutionary convergence among species of the Superorder Xenarthra.
ABSTRACT
Tamandua mexicana is a mammal of the superorder Xenarthra geographically located between Mexico and Peru that remains insufficiently studied. These species are characterized by their movement, resting, and eating of termites and ants in arboreal and terrestrial environments, and therefore, their thoracic limbs have been adapted morphologically to move in these environments. Tamandua mexicana is a species constantly threatened by different causes, and their thoracic limbs can be affected in the scapular and shoulder regions as a result; therefore, specific anatomical knowledge of the scapula allows for better clinical procedures, surgical approaches, radiological diagnosis and muscular reconstructions in extinct species of anteaters. The main objective of this study was to report the anatomical and radiographic features of the scapula in juvenile and adult specimens of T. mexicana. Gross dissections and radiographic study were performed in six cadavers. The scapula had large differences compared with other mammals, such as two spines, a foramen for the suprascapular nerve, a long acromion, a cranial transverse scapular ligament and caudolateral fossa for the origin of the muscles teres major, tensor fasciae antebrachii and subscapular. In juvenile specimens, a scapular cartilage, an acromial cartilage, craniomedial and caudolateral coracoscapular ligaments forming the foramen for the suprascapular nerve, and progressive ossification of those ligaments and the cranial transverse scapular ligament were observed. These findings were corroborated by radiography; therefore, these characteristics change with age. The bony reliefs of the scapula of T. mexicana corroborate the specialization of the shoulder in this species.
