text: There are various modifications according to the genera. A large hole may be present between the frontal bones and the basisphenoid (Psammophis, Coelopeltis); the maxillary may be much abbreviated and movable vertically, as in the Viperidae; the pterygoids may taper and converge posteriorly, without any connection with the quadrate, as in the Amblycephalidae; the supratemporal may be much reduced, and wedged in between the adjacent bones of the cranium; the quadrate may be short or extremely large; the prefrontals may join in a median suture in front of the frontals; the dentary may be freely movable, and detached from the articular posteriorly.
  The deviation from the normal type is much greater still when we consider the degraded wormlike members of the families Typhlopidae and Glauconiidae, in which the skull is very compact and the maxillary much reduced. In the former this bone is loosely attached to the lower aspect of the cranium; in the latter, it borders the mouth and is suturally joined to the premaxillary and the prefrontal. Both the transverse bone and the supratemporal are absent, but the coronoid element is present in the mandible.
  Joints of the snake skull
  Red A: the joint between the mandible and quadrate. It is analogous to the joint in mammalian jaws.
  Red B: the joint between the quadrate and the supratemporal. It is highly mobile in most directions, allowing a wider gape (i.e., the snake can open its mouth wider) and greater jaw flexibility.