Koutsiaris, E. A., C. Alamanis, A. Eftychiadis, and A. Zervas. “Castrati Singers: Surgery for Religion and Art”. Italian Journal of Anatomy and Embryology, vol. 119, no. 2, Nov. 2014, pp. 106-10, https://oajournals.fupress.net/index.php/ijae/article/view/1221.