Eyes very small; head not distinct; ventral scales scarcely enlarged; tail extremely short, ending obtusely and covered with peculiar scales. .......... Uropeltidae.
With vestiges of the hind-limbs appearing as claw-like spurs on each side of the vent; ventral scales transversely enlarged; eyes functional, free.
Ventral scales scarcely enlarged. .......... Ilysiidae.
Ventral scales transversely enlarged. .......... Boidae.
With a pair of poison-fangs in the front part of the mouth, carried by the otherwise toothless, much shortened, and vertically erectile maxillaries; ventral scales transversely enlarged; eyes free. .......... Viperidae.
All the remaining Snakes combine the following characters: the maxillaries are typical, not separately movable, horizontal, with a series of teeth.[[181]] The mandible is toothed but has no coronoid bone. There are no vestiges of limbs or of their girdles. The eyes are free.
Dentary movably attached to the tip of the articular bone of the mandible; skin beautifully iridescent. .......... Xenopeltidae.
Without a mental groove; the ends of the pterygoids are free, not reaching the quadrates. .......... Amblycephalidae.
With a median longitudinal groove between the shields of the chin; the squamosal is horizontally elongated, movable; the pterygoid reaches the quadrate. .......... Colubridae.
Fam. 1. Typhlopidae.–Burrowing snakes which have the whole body covered with uniform cycloid scales, and with the teeth restricted to the small and transversely placed maxillary bones. The pterygoids do not extend backwards to the quadrates, and there are no endopterygoids. The quadrates slant obliquely forwards, and are attached directly to the pro-otics, owing to the absence of squamosal bones. The prefrontals are in lateral contact with the nasals. There are vestiges of the pelvis, reduced to a single bone on each side. The eyes are hidden by shields of the skin.