text: Quadrate longer than supratemporal; maxillary little longer than quadrate, nearly straight in front of prefrontal: Tarbophis
  2. Maxillary much abbreviated and erectile; supratemporal not half as long as skull; mandible much longer than skull; basioccipital with a strong process.
  Maxillary bone solid: Vipera.
  Maxillary bone hollow: Ancistrodon.
  The vertebrae number 130 to 500 - in the European forms 147 (Vipera ursinii) to 330 (Coluber leopardinus).
  Vertebrae and ribs
  A snake has from 175 to more than 400 vertebrae in its backbone. The means by which vertebrae are secured are twofold: either a ball and socket joint, or zygopophyses, which stick out from each vertebra to poke rear-pointing projections from the vertebrae ahead of it. This results in a spine well-adapted to the snake's method of movement.
  The vertebral column consists of an atlas (composed of two vertebrae) without ribs; numerous precaudal vertebrae, all of which, except the first or first three, bear long, movable, curved ribs with a small posterior tubercle at the base, the last of these ribs sometimes forked; two to ten so-called lumbar vertebrae without ribs, but with bifurcate transverse processes (lymphapophyses) enclosing the lymphatic vessels; and a number of ribless caudal vertebrae with simple transverse processes. When bifid, the ribs or transverse processes have the branches regularly superposed.