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 

 premaxillse are very small and rarely bear teeth; the 

 palatines are usually connected with the maxillae 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 maxillae, palatines, 

 and pterygoids, and very rarely on the premaxillae. The 

 fang-like teeth of venomous serpents are borne by the 

 maxillae, and are few in 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 vertebrae 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 



