Gross anatomical adaptations of the craniolateral forearm muscles in Tamandua mexicana (Xenarthra: Myrmecophagidae): development of accessory muscles and rete mirabile for its arterial supply

Paula Valentina Polania-Guzmán,Juan Fernando Vélez-García

doi:10.1016/j.heliyon.2019.e02179

Paula Valentina Polania-Guzmán, Juan Fernando Vélez-García

Open Access

https://doi.org/10.1016/j.heliyon.2019.e02179

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Journal: Heliyon	Publication Date: Aug 1, 2019
Citations: 7	License type: cc-by

Affiliation: University of Tolima

Abstract

The northern tamandua (Tamandua mexicana) is a xenarthran mammal with a distribution from Mexico to Peru. This species arrives to wildlife care centres due to illegal trafficking and attacks by domestic dogs, both of which are situations where the northern tamandua's thoracic limbs (forelimbs) can be affected. As such, it is necessary to have anatomical studies that allow us to perform better medical and surgical procedures. Among these, studies about the musculoskeletal system also aid in the muscular reconstructions of extinct species. The aim of this study was to characterize the craniolateral muscles of the forearm in Tamandua mexicana and compare them with other Xenarthrans to determine their gross adaptations. Six dead specimens were used, and none were sacrificed for the purpose of this investigation. In five specimens, arterial repletion was done. Four were fixed with 10% formaldehyde and 5% glycerin, and two were dissected in fresh. All were dissected in the Veterinary Anatomy Laboratory of the Universidad del Tolima. The weights of the muscles from seven forearms were taken and divided in three functional groups for comparison with non-parametric statistics. Two muscular groups were found: one superficial formed by the brachioradialis, brachioradialis accesorius, extensor carpi radialis, extensor digitorum communis, extensor digitorum lateralis and extensor carpi ulnaris; and one deep muscular group formed by the supinator, extensor digiti III et IV, abductor digiti I longus, and extensor digiti I et II. They were supplied by different branches of the cranial interosseous, transverse cubital and superficial brachial arteries, which had the shape of rete mirabile; and all muscles were innervated by the deep branch of the radial nerve. The presence of the brachioradialis accesorius muscle in this species allows its hand to remain in semi-supination when it is mobilized in a quadrupedal manner. It must also support elbow flexion together with the action of the brachioradialis and the extensor carpi radialis muscles. All the antebrachial digital muscles sent tendons for the digit III making it the most functional for different grip activities such as climbing trees and searching for its food, however, the most strength was directed to supination and carpal extension, and therefore also to the flexion of the elbow.

Highlights

The northern tamandua (Tamandua mexicana) belongs to the superorder Xenarthra and the family Myrmecophagidae, as it has characteristics that differentiate it from other mammals such as an extra joint in its lumbar vertebrae and its lack of teeth (Munao, 2001; Gaudin and McDonald, 2008; Hautier et al, 2018)
The superficial group was formed by the brachioradialis, brachioradialis accessorius, extensor carpi radialis, extensor digitorum communis, extensor digitorum lateralis and extensor carpi ulnaris muscles (Figs. 1A, 2)
The reported insertion (Taylor, 1978; Humphry, 1869) is similar to that found in T. mexicana, we considered them as independent muscles because their origins, insertions, innervations and arterial supplies were independent, and besides that, the two muscles were superficial and their position goes in a collateral form, where the lateral is directed for the radius and the medial (m. brachioradialis accesorius) for the caudomedial part of the forearm where it covers part of the flexor muscles

Summary

Introduction

The northern tamandua (Tamandua mexicana) belongs to the superorder Xenarthra and the family Myrmecophagidae, as it has characteristics that differentiate it from other mammals such as an extra joint in its lumbar vertebrae and its lack of teeth (Munao, 2001; Gaudin and McDonald, 2008; Hautier et al, 2018). It is distributed geographically from southern Mexico, reaching northwestern Colombia, northwestern Venezuela, western Ecuador and northwestern Peru (Tirira, 2007; Gardner, 2008; Superina et al, 2010; Nun~ez-Perez et al, 2011; Brown, 2011). They reproduce once a year at any time and their gestation period lasts between 130 and 150 days (Silveira, 1969), and the brood remains with its mother until it reaches one year of age (Nowak and Walker, 1999).

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