A tergum (Latin for "the back"; plural terga, associated adjective tergal) is the dorsal portion of an arthropod segment other than the head. The anterior edge is called the base and posterior edge is called the apex or margin. A given tergum may be divided into hardened plates or sclerites commonly referred to as tergites.:20 So, for example, in a thoracic segment, the tergum may be divided into an anterior notum and a posterior scutellum. Lateral extensions of a tergite are known as paranota (Greek for "alongside the back") or carinae (Latin for "keel"), exemplified by the by the so-called flat-backed millipedes of the order Polydesmida.
McCafferty, W.Patrick (1983). Aquatic entomology: the fishermen's and ecologists' illustrated guide to insects and their relatives. Jones & Bartlett Publishers, ISBN 0867200170, ISBN 978-0-86720-017-1. Accessed here through Google Books on 08 Jan 2010.