GROSS ANATOMY AND SURGICAL APPROACH TO THE HUMERAL SHAFT IN GIANT ANTEATER (MYRMECOPHAGA TRIDACTYLA)

Abstract

Anteater forelimbs are distinguished morphologically from domestic animals, especially due to their unique movement and their natural habits. A knowledge of the pectoral limb anatomy and the proper surgical approach are fundamental to success in osteosynthesis and other surgeries. This study aimed to describe the muscles and neurovascular structures of the pectoral limb and the surgical approach to the humeral shaft of the giant anteater ( Myrmecophaga tridactyla ). Dissections of the forelimbs of seven cadavers were performed to identify the major muscles and neurovascular structures. Three of these animals' contralateral forearms were used to simulate the surgical approach to the humeral shaft. Some specific characteristics of the muscle morphology were biceps muscle had two heads, triceps muscle had three heads, and there was an olecranon-epicondylar muscle. To expose the shaft of the humerus, it was necessary to incise the superficial pectoral muscle and separate the heads of the biceps muscle. Due to the anatomical characteristics of the humerus, the craniomedial approach was the most appropriate because it accommodated the anatomical peculiarities of the giant anteater.

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

“…In Myrmecophaga , the FDP has five heads: radial, ulnar, olecranon, humeral, and other heads originating from the TBMH tendon (Macalister, 1875a; Pouchet, 1867; Windle & Parsons, 1899), and it can connect the tendons to the digits I–IV (Macalister, 1875a; Pouchet, 1867) or II‐IV (Windle & Parsons, 1899). In two recent studies on Myrmecophaga , the TBMH was observed to be continuous with the FDP (García et al, 2019; Sesoko et al, 2016); however, the detailed description of these muscles was not provided. In Cyclopes didactylus , the FDPb and FDPls were absent in the FDP; therefore, the FDP in Cyclopes only has three common heads (humeral, radial, and ulnar) and connects tendons to digits II and III (Galton, 1869a; Humphry, 1869; Macalister, 1875a).…”

“…Several authors have reported that the FDPb in Tamandua was formed upon the fusion of the TBMH with the FDP based on an analysis of its origin from the humerus in Tamandua and Myrmecophaga (García et al, 2019; Macalister, 1875a; Sesoko et al, 2016; Taylor, 1978; Windle & Parsons, 1899), and the innervation pattern was not considered. In a study on the brachial plexus in T. tetradactyla , the authors mentioned that TBMH was innervated by the ulnar nerve (Cruz et al, 2012).…”

“…In three earlier studies on genus Tamandua (Macalister, 1875a; Taylor, 1978; Windle & Parsons, 1899), and two current studies on genus Myrmecophaga (García, Pulido, & Soto, 2019; Sesoko, Rahal, Bortolini, Merlini, & Teixeira, 2016), the authors considered that the TBMH is fused to the FDP because the humeral origin area of the TBMH compared to that of other mammals is occupied by the FDP; however, the studies did not examine the muscle innervation. To study the evolution of a muscle, it is important to review its origin, insertion, and innervation (Kawashima et al, 2017).…”

Anatomy and surgical approach to the humerus, radius and ulna of common sloth (Bradypus variegatus)

“…It's almost straight structure differs from domestic animals, in which the humerus has a spiral shape due to the sulcus m. brachialis (KÖNIG & LIEBICH, 2021). The distal extremity of the humerus is flattened craniocauldally, as observed in the anteater, presenting developed epicondylus that offer great area for fixation of the powerful flexor and extensor muscles of the carpus and the fingers (SESOKO et al, 2016).…”

“…As for the musculature of the arm of B. variegatus, M. latissimus dorsi origin had its origin from the posterior half of the spinal processes of the thoracic vertebrae inserting medially in the proximal portion of the humerus, as described by NYAKATURA & FISCHER (2011) for the sloths Choloepus didactylus and Bradypus variegatus. Some fibers of the M. latissimus dorsi extend as a continuation to M. tensor fasciae antebrachii, which is inserted into the olecranon, similar to the giant anteater (SESOKO et al, 2016) The M. triceps brachii consisted of two heads, lateral and longum, which originated at the caudal end of the scapula (caput longum) or at the proximal end of the humerus (caput laterale) and were inserted into the Tuber olecrani. MILLER (1935) described three caputs for the genus Bradypus (laterale, longum and mediale), as well as for equine, bovine and swine (KÖNIG & LIEBICH, 2021).…”