6io REPTILIA. 



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 

 premaxillae 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 

 is much elongated ; the kidneys are not opposite one 

 another. 



The poison is useful in defence, and in killing the prey, 

 which is always swallowed whole. It is interesting to notice 

 a recent discovery, requiring amplification, that the bile of 

 a poisonous snake is an antidote to its venom. 



