LACERTILIA, 15s-er-tilla, or AUTO SAURI, the order of saurian reptiles which contains the lizards. These are distinguished from the serpents (Ophidia), to which they are most nearly allied by the fact that the right and left halves of the mandibles (lower jaws) are connected by a sutural syrpphysis, whereas those of serpents are connected by a more or less distensible cartilage. The great majority possess well-developed limbs, movable eyelids and cutaneous scales, covered by a horny epi dermis, usually thin, hut sometimes thick and rising into pointed projections. In a few de graded and burrowing forms the limbs have been greatly reduced, or one pair or even both pairs completely lost, while the eves may have become buried beneath the skin and the scales nearly or wholly obsolete. The vertebrae are proccelous, except in some of the geckos, where they are amphicrelous; the ribs of the trunk ar ticulate by their capitular heads only, the re duced tubercula being attached to the vertebrae by ligaments. The limbs are typically formed after the pentadactyl pattern; and the shoulder girdle and sternum are complete. The hyoid apparatus resembles that of birds. In the skull the quadrate bone is movable except in a few degraded forms. The skin is covered with scales formed within it, and the epidermis is horny ?rid is periodically shed in flakes; hut in many cases these scales do not overlap and look like scales, hut are represented by bony granules, giving a "pebbly" aspect to the sur face; or these osteoderms (which never occur in snakes) may form in the ordinary scales. The skin contains no glands; but in many liz ards abounds in chromatophores (q.v.) con trolled by muscles whose action causes the va riations in surface color of which many lizards arc capable and of which they avail themselves as an aid in hiding from their enemies. In their reproduction lizards never undergo any metamorphosis and are generally oviparous, but in some the eggs are retained until they hatch within the abdomen of the mother. Sali
vary glands are found which in Heloderma act as poison glands. The lungs are thin-walled sacs, from which terminal pouches may arise. The movement of the ribs assists in respiration. The lizards are most abundant in tropical re gions, but are absent only from the cooler tem perature and the frigid regions of the globe. The group possesses strong power of regenerat ing lost parts and especially of renewing the tail, which in many families breaks off under a very slight strain.
Fossil History.— The Lacertilia are a comparatively recent development of the rep tilian race, not traceable beyond the beginning of the Tertiary. Fragmentary remains of sev eral existing families occur in the Eocene and Miocene rocks; and the Pleistocene river-de posits of Queensland, among which was a monitor-lizard 30 feet long. The line prob ably originated in the Prosauria (q.v.), repre sented by a single living form — the tuatera (q.v.). Lizards are now scattered over all the warmer parts of the world and seem to be in creasing and developing. They are said by Hoffman to include 434 genera and 1,925 species.
Classification.— The Lacertilia are di vided into three sub-orders, of which the fol lowing is an outline: Sub-order 1. Geckones.— Lacertilia with four legs, amphiccelous vertebrae and• clavicles dilated ventrally. The chorda petsists and grows throughout life, in the centre of and between the vertebrae; the ribs are bifurcated, and dentition is pleurodont. Some species have mechanically adhesive discs. The one family (Geckonidce) is coextensive with the sub-order. This is a very old group, modern species exist ing in tropical and southern European countries.
See GECKO.
Sub-order 2. Lacertm.—Laccrtilia with proccelous vertebra and the ventral part of clavicles not dilated. Eighteen families, as fol lows: 1. family of exclusively Old World lizards, containing some 200 species, among which the Malayan dragon (q.v.), and the frill-lizard (q.v.) are remarkable species. Many have a very chameleon-like appearance.