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.