Is the Articularis Humeri Muscle Homologous to the Coracobrachialis Muscle in Carnivorans? An Evolutionary and Terminological Answer Based on the Shoulder Myology of the Coati (Nasua nasua, Carnivora, Procyonidae).

South American coati (Nasua nasua) is a carnivoran of the suborder Caniformia and family Procyonidae. Anatomical and functional studies have been performed on the thoracic limb muscles of this species. The topology and innervation are necessary to establish a more suitable anatomical terminology and to infer the muscle evolutionary derivation in anatomical studies. Within the shoulder muscles, the articularis humeri muscle is found caudal to the shoulder joint capsule and is innervated by the axillary nerve. The coracobrachialis muscle is medial and is innervated by the musculocutaneous nerve. However, some studies in N. nasua and other carnivorans describe the coracobrachialis muscle with the name articularis humeri muscle. Therefore, the present study aimed to analyse the terminology and evolutionary derivation inferences of the shoulder intrinsic muscles in N. nasua based on their attachments, topology, and innervation. We dissected 15 thoracic limbs from eight formaldehyde-fixed specimens. Most muscles conserved the evolutionary derivation proposed to other procyonids. Ten limbs presented the articularis humeri muscle similar to that described in the ursid Ursus maritimus (polar bear) and the felids Felis catus (domestic cat) and Panthera leo (lion). This muscle could have derived from the subscapularis muscle and potentially be present in the last common ancestor of carnivorans. Based on most references in myological studies of Carnivora, the present study is the first record of the presence of the articularis humeri muscle in N. nasua. Therefore, the name m. articularis humeri should not be used as a synonym or homologous muscle to the coracobrachialis or coracobrachialis brevis.