Anatomical and radiographic study of the scapula in juveniles and adults of Tamandua mexicana (Xenarthra: Myrmecophagidae)

Origin and Distribution of the Brachial Plexus Nerves in Northern Tamandua (Tamandua mexicana)

Tamandua mexicana is a species of the superorder Xenarthra that is found in many regions of Mexico, Peru, Colombia, Ecuador and Venezuela. This species is important because it is a model for comparative studies of the evolutionary anatomy of xenarthrans. However, there are few anatomical studies on which to base these areas, such as the anatomy of the brachial plexus. Several studies use the brachial plexus anatomy for phylogenetic analysis and medical procedures. Thus, this study aimed to describe the origin and distribution of the brachial plexus in T. mexicana. Twelve specimens of T. mexicana fixed in formaldehyde 4% were dissected. The ventral spinal nerves from C5 to T2 originated the brachial plexus. In most cases, C5-C7 formed the cranial trunk, C6-C7 the middle trunk and C8-T1 the caudal trunk. In all specimens, these trunks joined and formed the common trunk, which distally divided into two divisions: dorsal and ventral. The pectoralis cranialis, pectoralis caudalis, thoracicus longus, thoracicus lateralis and thoracodorsalis nerves supplied the extrinsic thoracic limb muscles. The innervation for the intrinsic thoracic limb muscles was supplied by the suprascapularis, subscapulares, axillaris, musculocutaneus, radialis, medianus and ulnaris nerves. The intercostobrachialis, axillaris, radialis, ulnaris, medianus and caudal cutaneous antebrachial nerves innervated the skin of this species. The trunks and divisions were similar comparatively to those reported in other xenarthrans. However, T. mexicana was more similar to sloths. This suggests a phylogenetic trade in their evolution. The origin and distribution of the brachial plexus nerves resembled those of the other Xenarthras, which can assist in medical procedures within the superorder.

Evolutionary anatomical and functional characteristics of the intrinsic shoulder and brachial muscles in the northern anteater (Tamandua mexicana)

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.

Anatomical, morphometric and radiographic study of the humerus in lesser anteater (Tamandua mexicana Saussure, 1860): terminological and functional analyses

Tamandua is a neotropical mammal genus that belongs to the superorder Xenarthra. The thoracic limbs of Tamandua have anatomical adaptations that widely differ from other mammals, and there are frequently specimens in wildlife care centers with traumas in their limbs. However, there are few studies describing the radiographic and morphometric anatomy of the humerus in Tamandua, or describing partially the bone reliefs. Thus, the main objective of this study was to describe the characteristics of the humerus of Tamandua mexicana based on gross dissections, radiographies and measurements comparing with other studies in the three Vermilingua genera, and establishing more suitable terminology. Twelve thoracic limbs of six death specimens of Tamandua mexicana were analyzed. The bone reliefs, ligaments, muscles and neurovascular structures related to the humerus were identified, and the suitable terminology to the humerus of Tamandua was established. Morphometric measurements of each bone relief were taken, and the data were statistically analyzed with the Wilcoxon non-parametric test for functional proposes. The humerus of Tamandua has anatomical characteristics mainly to offer greater areas to the muscles that act on the shoulder flexion and hand movements. Even the articular reliefs are lesser than the adjacent non-articular reliefs, the muscles and ligaments are the anatomical structures that give more stabilization to the shoulder and elbow joints. The deltosupracondylar ligament can be partially ossified in older adult specimens, and neurovascular structures pass through the supracondylar foramen. These anatomical characteristics must be accounted for in the radiological diagnosis and surgical approaches.

Evolutionary adaptations in the flexor digitorum profundus muscle in Tamandua mexicana (Xenarthra, Myrmecophagidae)

The northern tamandua (Tamandua mexicana) is a neotropical mammal of the order Pilosa, suborder Vermilingua, and family Myrmecophagidae. This species has anatomical and functional adaptations in its forelimb for semiarboreal quadrupedal locomotion. Several studies have reported that the medial head of the triceps brachii and flexor digitorum profundus muscles are fused in species belonging to the family Myrmecophagidae. However, there is no reference to the innervation in these. The triceps brachii muscle is commonly innervated by the radial nerve and the flexor digitorum profundus muscle by the ulnar and median nerves. This study aims to describe the gross anatomy of the flexor digitorum profundus muscle in Tamandua mexicana with respect to the shape, origin, insertion, innervation, and arterial supply. Both forelimbs of nine specimens were used, which were dissected from superficial to deep layers. The formalin-fixed caudomedial forearm muscles were weighed, and the weight percentages of individual forearm muscle specimens were calculated. The flexor digitorum profundus had the highest weight among the forearm muscles and consisted of five heads (three humerals, one radial, and one ulnar). These heads were innervated by median and ulnar nerves; therefore, based on the innervation pattern, we concluded that the medial head of the triceps brachii muscle is not fused with the flexor digitorum profundus. Therefore, the flexor digitorum profundus muscle is highly developed in Tamandua and occupies the caudal part of the arm and forearm, which is an evolutionary adaptation that could have occurred during evolution from the common ancestor of Tamandua and Myrmecophaga.