Complex sentence: All viperines have a pair of relatively long, solenoglyphous (hollow) fangs, that are used to inject venom from glands located towards the rear of the upper jaws.
Split into simpler sentences: All viperines have a pair of relatively long, solenoglyphous (hollow) fangs, that are used to inject venom. The venom comes from glands located towards the rear of the upper jaws.