Morphology studies provide knowledge that allows us to understand how animals interact with their natural environment or in captivity. In this context, comparative anatomy on the formation of the brachial plexus has been a matter of interest since the 19th century, and remains one of the most intriguing topics of contemporary anatomy. The aim of this study was to describe the origin and the antimeric distribution of the brachial plexus nerves in Macaca mulatta, as well as the muscles innervated by it. Ten male rhesus monkeys (Macaca mulatta) were used. Animals came from the Laboratory Animals Breeding Centre (Cecal/Fiocruz), and were donated to the Animal Anatomy Department of the Universidade Federal Rural do Rio de Janeiro. Specimens were fixed in formaldehyde by infusion of a 10% solution. They were subsequently kept in low-density polythene containers with 500 L of 30% formaldehyde over a period of 12 months. In 11 plexus (55%) the resulting nerves were constituted by the connections between the ventral spinal branches C5, C6, C7, C8 and T1. In five plexus (25%), the participant roots were C4, C5, C6, C7, C8, T1 and T2. In two (10%) plexus, they were C5, C6, C7, C8, T1 and T2. In the other two (10%) plexus it was observed to be formed from C6, C7, C8, T1 and T2. The ventral branches formed three nerve trunks: cranial, middle and caudal. The suprascapular, subscapular, axillary, musculocutaneous, radial, median and ulnar nerves innervated the intrinsic muscles. The subclavian, thoracodorsal, medial cutaneous nerve of the arm and forearm, long thoracic, cranial pectoral and caudal pectoral innervated extrinsic muscles. Results obtained in this study contribute to the field of comparative anatomy of primates, and provide information for applied research, serving as a basis for clinical and surgical procedures that use this species as a model animal.
