The Primo-Vascular System https://www.hindawi.com/journals/ecam/2015/361974/ https://www.hindawi.com/journals/ecam/2015/303769/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3793287/ https://jaoa.org/article.aspx?articleid=2480724 https://www.sciencedirect.com/science/article/pii/S2005290113002082