frontal suture
From ZooTerms (Dictionary of Invertebrate Zoology)
frontal suture: 1. One of two sutures arising at the anterior end of the coronal suture which extends ventrad toward the epistomal suture.
2. In Diptera, a suture shaped like an inverted “U”, having the base crossing the face above the bases of the antennae, and the arms extending downward on each side of the face; a ptilinal suture.
