Evolutionary comparative analysis of the extrinsic thoracic limb muscles in three procyonids (Procyon cancrivorus Cuvier, 1798, Nasua nasua Linnaeus, 1766, and Potos flavus Schreber, 1774) based on their attachments and innervation.

The procyonids (Procyon cancrivorus, Nasua nasua and Potos flavus) are Neotropical carnivorans with the ability to climb trees; however, each one has different locomotor preferences. Thereby, P. flavus is highly arboreal, P. cancrivorus is mainly terrestrial with abilities to swim, and N. nasua is also fossorial. These activities not only require movements of the hands but stabilize the thoracic limb, an action performed by the extrinsic muscles. Besides, former descriptions performed in procyonid species have obsolete terms for these muscles, generating confusion about the comparison among species. Thereby, muscle innervation has also been used to support the evolutionary derivation of the muscles. Therefore, this study aimed to describe the attachments and innervations of these muscles in three procyonids. There were intra- and interspecific anatomical variations in the attachments of all extrinsic thoracic limb muscles. However, based on the innervation, several evolutionary derivations in procyonids could be found, such as: the cleidobrachialis muscle derived from the deltoideus muscle; the atlantoscapularis muscle of P. flavus derived from the serratus ventralis cervicis muscle; the pectoralis transversus muscle derived from the pectoralis profundus and superficiales muscles; and the pectoralis abdominalis muscle derived from the cutaneus trunci muscle. Some functions could be associated with locomotor habits, among them a highly developed pectoralis abdominalis in Nasua for its fossorial habits and the atlantoscapularis in Potos for its arboreal and prehensile habits. Thus, the extrinsic muscles in procyonids have evolved for locomotor preferences, but mainly due to their phylogenetic relationship within the family Procyonidae.