Origin and Distribution of the Brachial Plexus in Two Procyonids (Procyon cancrivorus and Nasua nasua, Carnivora)

SIMPLE SUMMARY: The brachial plexus is a nervous network from which nerves originate to innervate the thoracic limb and its adjacent parts. It has been found with different origins and distributions in the thoracic limb between carnivoran species (interspecific) and even in the same species (intraspecific). Anatomical knowledge of the brachial plexus allows us to understand the differences and similarities between species to be applied in evolutionary biology. Procyon cancrivorus and Nasua nasua are two neotropical carnivoran species that have different evolutionary adaptations in their thoracic limbs. The aim of this study was to describe the anatomical arrangement of the brachial plexus of these species to review intra- and interspecific anatomical variations. The brachial plexus may originate in both species from the last four cervical spinal nerves (C5, C6, C7 and C8) and the first two thoracic spinal nerves (T1 and T2). The contribution from C5 was higher in Nasua nasua, while the contribution from T2 was higher in Procyon cancrivorus. Interestingly, both species develop ansa axillaris and ansa pectoralis, which is a primitive anatomical arrangement that is shared with other members of arctoid carnivorans. Therefore, this study confirmed that both structures can be present in some wild carnivorans. ABSTRACT: Procyon cancrivorus and Nasua nasua are two procyonids with different evolutionary adaptations to use their thoracic limbs. Therefore, this study aimed to characterize the differences in the brachial plexus between both species. Five P. cancrivorus and five N. nasua cadavers were used to perform this investigation with the permission of the bioethics committee and environmental license. Gross dissections were performed on the cervical, pectoral, and thoracic limb regions to find the origin and distribution of the brachial plexus. The brachial plexus of both species originated in a variant manner from C5-T1, C5-T2, C6-T1, or C6-T2. All brachial plexus nerves were observed and, interestingly, the musculocutaneous sent a communicating branch to the median nerve medially to the axillary artery, forming an ansa axillaris in both species. An ansa pectoralis was also observed medially to the axillary artery. Additionally, in P. cancrivorus, the musculocutaneous nerve innervates the pronator teres and flexor carpi radialis muscles and communicates with the median nerve at the elbow level to continue as a common trunk at the antebrachium. The brachial plexus has differences between both procyonids, although in both species, it could conserve a primitive arrangement present within the infraorder Arctoidea.