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

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.

An unusual relationship between the axillary artery and brachial plexus in a cross-breed dog cadaver: a proposal for revising the terminology for nerve loops

“…2a-c). The formed nerve loop traversed by a portion of the axillary artery has been called 'ansa pectoralis' based on the nomenclature presented by the authors of several studies on carnivorans though it has not been used in the NAV [8,9,11,12]. Put simply, if the pectoral loop is present, the axillary artery passes through it.…”

“…Finally, a revision to the terminology of the nerve loops of the brachial plexus was prompted by this case since the current terminology does not exactly address the structural nature of these loops, especially when their variants are encountered. As a communicating branch of the musculocutaneous nerve to the median nerve, the term ansa axillaris has been proposed by some authors working on carnivorans including the domestic dog [7][8][9]. Nevertheless, in the study of Davis on some arctoid carnivores, the presence of such communication has been defined as ansa mediana in the Ailurid Ailurus fulgens, the Ursid Ursus americanus, and procyonids Procyon lotor and Potos flavus [12].…”

“…The traces of such communicating branches extending to the caudal pectoral nerves can only be found in the illustrations of Miller's Anatomy [1]. With a comparison of the nerve loops in other studies on carnivorans and those in the current case, it seems that the terminology needs some revisions to address what they mean exactly [7][8][9].The aim of the present case report is to introduce an unusual anatomical relationship between the axillary artery and brachial plexus identified in an adult female cross-breed dog cadaver and to propose a revision of nomenclature on the nerve loops of the brachial plexus.…”