Lizard heads called the parietal eye, a basal ("primitive") feature also present in the tuatara. This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps them detect predators stalking it from above. Until 2006 it was thought that among lizards, only the Gila monster and the Mexican beaded lizard were venomous. However, several species of monitor lizards, including the Komodo dragon, produce powerful venom in their oral glands. Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its
Southern alligator lizard the fact that the back and belly scales of these lizards are reinforced by bone, as they are in alligators. Three subspecies can be distinguished: the California alligator lizard ("E. m. multicarinata"), the San Diego alligator lizard ("E. m. webbii"), and the Oregon alligator lizard ("E. m. scincicauda"). The subspecific name "webbii" is in honor of Thomas Hopkins Webb (1801–1866) who was Secretary of the United States and Mexican Boundary Survey (1848–1855). The subspecific name "scincicauda" means "skink tail". The southern alligator lizard measures from 3 to 7 inches (7.3 - 17.8 cm) in snout-to-vent length (SVL). Including tail, it