Mediolateral axis : In animals with bilateral symmetry an axis orthogonal to the rostrocaudal axis that lies in the frontal plane (Henle, 1855). It is unusual in having a right and left half reflected across the median plane (Henle, 1855); that is, for the right and left sides of the body, medial (Schulze, 1893) is toward the median plane and lateral (Barclay, 1803) is toward the right or left edge of the body. A synonym is right-left axis; see Kuhlenbeck (1973, p. 112).