Due to the absence of literature on the brachial plexus in the Spix's yellow-toothed cavy, this study was conducted to examine the origin and neural distribution of this rodent's brachial plexus. Ten adult animals obtained from previous experiments were thawed, fixed in 10% formalin solution for 72 h and then dissected. Cotton blocks soaked in 2% hydrogen peroxide were placed on the ventral roots of the plexus. Photographs of the most representative specimens were taken and schematic sketches were prepared to illustrate the results. The Spix's yellow-toothed cavy's brachial plexus primarily originated from the ventral roots of the sixth (C 6 ), seventh (C 7 ) and eighth (C 8 ) cervical nerves and from the first two thoracic nerves (T 1 , T 2 ), and less frequently from C 6 -T 1 or C 6 -T 3 . The peripheral nerve trunks of the Spix's yellow-toothed cavy's brachial plexus are the following: suprascapularis (C 6 -C 7 ), axillaris (C 6 -C 7 ), subscapulares (C 6 -C 7 ), cranial pectoral (C 6 -C 7 ), musculocutaneous (C 7 -C 8 ), radialis (C 7 -T 2 ), medianus (C 7 -T 2 ), ulnaris (C 7 -T 2 ), pectorales caudales (C 7 -C 8 ), thoracicus longus (C 7 -C 8 ), thoracicus lateralis (C 7 -T 2 ) and thoracodorsalis (C 7 -T 2 ).Keywords: anatomy; brachial plexus; nervous system; rodent; Galea spixii List of abbreviations C 6 = ventral root of C 6 ; C 7 = ventral root of C 7 ; C 8 = ventral root of C 8 ; T 1 = ventral root of T 1 ; T 2 = ventral root of T 2 ; T 3 = ventral root of T 3