The crab-eating fox (Cerdocyon thous) is a wild canid distributed in South America, which is susceptible to traumas caused by captors, accidents on roads, and traps. Due to these events their thoracic limbs can be involved at the level of the forearm, therefore, knowledge of the gross anatomy of its muscles is important in order to develop clinical and surgical procedures at this level compared with the domestic dog. The main objective of this investigation was report the intra and interspecific anatomical variations of the caudomedial forearm muscles in Cerdocyon thous in comparison mainly with the domestic dog. Six dead specimens from wildlife care centres of CORPOCALDAS were used. These were fixed with a solution of formaldehyde, mineral oil and phenic acid. Both thoracic limbs of each specimen were dissected from superficial to deep, emphasizing the caudomedial part of the forearm in order to review the anatomical characteristics of each muscle. These muscles were similar to those reported in the domestic dog, but some variations were observed such as the innervation of the pronator teres muscle by the musculocutaneous nerve in a specimen unilaterally; the formation of an accessory muscle from the ulnar head of the flexor carpi ulnaris muscle in most specimens; and the vestigial presence of the anconeus epitrochlearis muscle in a specimen bilaterally.