Fig. 12.

a Combination of neural extension, mouth contraction and ventral contraction, generating a quite flexed head with an important neck curvature. The ventral contraction hinders the mouth invagination. We see that the shape of the lower and upper jaws are different because of the different traction forces. b Combination of neural extension, mouth tension, and moderate ventral contraction giving a more elongated pattern, a flatter head with little flexure, and a more pronounced mouth invagination. c Combination of neural extension and mouth contraction, giving and inward rotation and invagination of the mouth. Video 17. d Combination of asymmetrical mouth contraction and DV contraction. The asymmetry of mouth contraction generates an asymmetry in upper vs lower jaws. e Combination of dorsal extension, mouth contraction, and ventral contraction, provoking an inversion of curvature between the head and the neck