Potential Lack of Association Between Three Vestigial Muscles in Humans: A Willed Body Donor Study

Purpose: Anatomical agenesis within a population is not well understood, with variations including but not limited to complete absence, unilateral presence, or bilateral presence. Agenesis of human vestigial muscles including the palmaris longus (PL), fibularis tertius (FT), and psoas minor (PM) has been studied; however, the relationship between their presence and absence has not been examined. The purpose of this study is to analyze the prevalence of the PL, FT, and PM muscles, investigate any relationship of prevalence based on sex or race, and investigate any correlation between the presence or absence of each muscle within individual donors. Methods: Twenty-three willed body donors were comprehensively dissected by medical students, and the presence or absence of the PL, FT, and PM muscles was recorded. Results: The PL was present bilaterally in 87% of donors and absent bilaterally in 13%. The FT was present bilaterally in 96% of donors, and present unilaterally in 4% of donors. There was no evidence of total agenesis of the FT within our sample. The PM was present bilaterally in 39% of donors, and absent bilaterally in 61% of donors. No statistically significant relationship was indicated between muscle presence and the sex or race of the donors. No correlation between the presence or absence of each of the muscles was found. Conclusion: In this sample of willed body donors, there was no relationship between muscular agenesis of the vestigial muscles. This suggests that muscle agenesis is a local genetic developmental event at each muscle, and that there is not a single developmental event that leads to agenesis of multiple vestigial muscles. Further understanding of the agenesis of vestigial structures within populations and subpopulations can aid in physician diagnosis and understanding of the anatomical makeup of individuals.