Lacking appendages, snakes have simple bodies that consist of a head, body and tail. Additionally, some snakes exhibit a narrowing immediately behind the head, which gives them a discernible neck as well. Some primitive snake lineages, such as boas and pythons, have retained their pelvic girdle. Inspecting the tail of such snakes reveals tiny claws or spurs, which are the remnants of rear legs once attached to their pelvises.
Snakes have several unique body parts. The opening to a snake’s intestinal tract is called the vent. The vent is identified by noting a large, semi-circular scale near the posterior end of the snake. The tail of a snake starts at the vent, and extends to the end of its body. Different species have evolved different types of tails. Tree-dwelling species, such as green tree pythons, have exceptionally long tails that help them grip branches. In contrast, ground-dwelling species, such as kingsnakes, have relatively short tails. Rattlesnakes have evolved tails that produce a noise when shaken.
Snakes have no external ear openings, although they do have a few internal ear structures. Snakes lack eyelids; instead, they have clear scales, called spectacles, to cover their eyes. This protects their eyes and keeps them from drying out. Many boas and pythons have dimples in their lip scales, which allow them to detect heat from their environment.