Origin, Development, and Evolution of Primate Muscles, with Notes on Human Anatomical Variations and Anomalies

This chapter presents a comparative study that focuses on the muscles of the trunk, pelvis, and lower limb. It draws together the broader evolutionary and developmental implications of the study of the musculature of primates. The chapter also discusses in more detail the origin, ontogeny, and evolution of the head, neck, pectoral, and forelimb muscles. Concerning the head and neck muscles, studies using rhombomeric quail-to-chick grafts to investigate the influence of hindbrain segmentation on craniofacial patterning showed that each rhombomeric neural crest cell population remains coherent throughout ontogeny, with rhombomere-specific matching of muscle connective tissue and their attachment sites for most head and neck muscles. Limbs with digits first appeared in aquatic taxa with more than five digits, but the transitions to terrestrial locomotion and to pentadactyly, and then to digit reduction in some clades, are particularly poorly understood.