A middle, thin muscular coat consists of smooth muscle fibres intersecting in different directions in which, however, an inner circular and an outer longitudinal layer can be distinguished to a certain degree. A rather thick inner mucous coat is covered by numerous transverse ridges known as the vaginal rugae (rugae vaginales). These ridges fold to form two longitudinal columns of the rugae (columnae rugarum) one of which passes in the middle of the anterior and the other on the posterior vaginal wal. The columns are developed best in the lower part of the vagina and disappear at the top. icd 10 training.