Our poisonous Texas snakes belong to two families—the _Viperidae_
(subfamily _Crotalinae_—pit vipers) and the _Elapidae_ (cobra-like
snakes). The pit vipers, which include rattlesnakes, copperheads and
cottonmouths, possess an opening on either side of the head, between the
eye and the nostril. With these heat-sensitive pits, the snake can
locate warm-blooded prey in the dark and make a direct hit upon a rat or
mouse which it cannot see.
[Illustration: Snake skeletons]
Snakes belonging to this family are further characterized by the
possession of elliptical eye pupils, somewhat triangular-shaped heads
and long, movable fangs in the front of the upper jaw. Each fang is
connected by a tube to the poison gland located just behind the eye.
When the snake is at rest and its mouth is closed, the fangs lie folded
back against the roof of the mouth. During the strike, the mouth is
opened so that the upper and lower jaws form an angle of nearly 180
degrees. The fangs are then erected to point almost directly forward.
With the fangs in this position, the strike results in a stabbing action
rather than a true bite.