Rhomboid Major Muscle - Evolutionary Variation

Evolutionary Variation

The muscles of the shoulder can be categorized into three topographic units: the scapulohumeral, axiohumeral, and axioscapular groups. Stretching from the spine to the scapula, rhomboid major forms part of the latter group together with rhomboid minor, serratus anterior, levator scapulae, and trapezius. The trapezius has evolved separately, but the other muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae (homologous to the ribs). Functional demands has resulted in the evolution of individual muscles from the basal unit formed by the serratus anterior. In primitive life forms, the main function of the axioscapular group is to control the movements of the vertebral border of the scapula: fibers concerned with the dorsal movement of scapula evolved into the rhomboids, those with ventral motion into serratus anterior, and those with cranial movements into levator scapulae.