632  REPTILLA 
used as limbs in locomotion, being attached to the large 
ventral scales which grip the ground. In the caudal region 
the transverse processes, which are elsewhere very small, 
take the place of ribs. 
One of the most distinctive characteristics of the skull 
is the mobility of some of the bones. Many of the Ophidians 
swallow animals which are larger than the normal size of 
the mouth and throat. The mobility of the skull bones is 
an adaptation to this habit. Thus the rami of the mandible 
are united by an elastic ligament; the quadrates and the 
squamosals are also movable, forming ‘‘a kind of jointed 
lever, the straightening of which permits of the separation 
of the mandibles from the base of the skull.” The nasal 
region may also be movable. On the other hand, the 
bones of the brain-case proper are firmly united. The 
premaxille are very small and rarely bear teeth; the 
palatines are usually connected with the maxille by trans- 
verse bones, and through the pterygoids with the movable 
quadrates. 
Teeth, fused to the bones which bear them, occur on the 
dentaries beneath, and above on the maxillz, palatines, 
and pterygoids, and very rarely on the premaxille. The 
fang-like teeth of venomous serpents are borne by the 
maxillz, and are fewin number. Each fang has a groove 
or canal down which the poison flows. When the functional 
fangs are broken, they are replaced by reserve fangs which 
lie behind them. In the egg-eating African Dasypeltis the 
teeth are rudimentary, but the inferior spines of some of 
the anterior vertebree project on the dorsal wall of the 
gullet, and serve to break the egg-shells. 
When a venomous snake strikes, the mandible is lowered, 
the distal end of the quadrate is thrust forward (this pushes 
forward the pterygoid), the pterygo-palatine joint is bent, the 
maxilla is rotated on its lachrymal joint, the fangs borne by 
the maxilla are erected into a vertical position, the poison 
gland is compressed by a muscle, and the venom is forced 
through the fang. 
Some of the peculiarities in the internal organs of Ophidia 
may be connected with the elongated and narrow shape of 
the body. Thus one lung, usually the left, is always smaller 
than its neighbour, or only one is developed; the liver 
