A generic caterpillar head for to showing anatomy.
Sulcus: generally means a depression of some sort, here the sulci are also cleavage lines. This means that the cuticle (exoskeleton) will split along these lines when the caterpillar molts.
Frontoclypeus: a plate of exoskeleton above the labrum.
Stemmata: larval eyes similar to ommatidia (the units of adult insects' compound eyes), but simpler.
Labrum: Sort of an insect upper lip.
Vertex: Forehead, more or less.
Gena: Area around and below the stemmata. The equivalent of cheeks on a human.
Setae: Hairs. Caterpillars gain more hairs every time they molt.
Mandible: Chompy bits.