(A) Normal nulligravid cervix. The external os is a small, smooth, circular opening. (B) Normal parous cervix. The external os is a large, transverse, stellate slit.
Modified from: Pritchard JA, MacDonald PC. Williams Obstetrics, 16th ed, Appleton-Century-Crofts, Prentice Hall, New York 1981. p.23.
