These muscles are mesodermal in embryologic origin. It deals with the anatomical, histological and embryologic terminology. Carcinoid tumors, particularly those derived from the embryologic foregut, occur in isolated cases. Amastia is presumably due to failure of embryologic mammary ridge development, or incomplete involution. There are conflicting views on the embryologic origin of the vagina. Vasculogenesis occurs during embryologic development of the circulatory system. Some authors have theorized that a persistent venous sinus reflects an arrest in embryologic development. The embryologic origin of the muscle is controversial and subject to numerous hypotheses. Embryologic mesenchymal cells (MSC) condense into layers of vascularized primitive connective tissue.