Repositorio Académico

The anatomical variation of the major pectoral muscles is infrequent, namely the agenesis of the pectoralis major muscle due to the morpho-functional alterations it causes. On the other hand, he presence of -supernumerary pectoral muscles is not common and its physiological, clinical or surgical importance will depend on the stage of its development. The important aspect is that these muscles, while crossing the anterior wall of the axila and inserting in the humerus, may confuse or difficult surgical access to the content of the axillary fossa. Pectoralis tertius muscles were found in two dissected cadavers at the Topographic Anatomy of the Faculty of Medicine of the Universidad de La Frontera, Chile. These muscles were bilateral and independent of the pectoralis major muscle. They originated in the external face of the sixth rib and adjacent regions, and inserted in the coracoid process, the crest of the greater tubercle of the humerus, or next to the insertion of the pectoralis major muscle, contributing to the formation of the anterior wall of the axila. The supernumerary muscles crossing the axillary region, whether in an arched form or elongated as the pectoralis tertius muscles, may confuse the surgeon at the entrance of the axila. In view of the above, it is always necessary to consider the possible existence of this type of anatomical variation.