CLASSIFICATION OF OPHIDIA. 581 



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. 



The British adder {Pelias derus) is viviparous, and so are a few others. 

 The great majority are oviparous, but confinement and abnormal con- 

 ditions may make oviparous forms, like the Boa constrictor and the 

 British grass-snake (Tropidonotus matrix), viviparous. The female 

 python incubates the eggs. 



Many Ophidians become lethargic during extremes of temperature, 

 or after a heavy meal. 



Though most abundant in the tropics, snakes occur in most parts of 

 the world. They are absent from many islands ; thus there are none 

 in New Zealand, and we all know that there are no snakes in Iceland. 

 Most are terrestrial, but not a few readily take to the water, and there 

 are many habitual sea-serpents. 



The serpent still bites the heel of progressive man, the number of 

 deaths from snake-bite in India alone amounting to many thousands 

 yearly, though there can be little doubt that the snakes are often 

 innocent scapegoats. 



True Ophidians first occur in Tertiary strata. 



Classification of Ophidia. 



Sub-order 1. Typhlopidse. The lowest and most divergent Ophidians, 

 occurring in most of the warmer parts of the earth, generally smaller 

 than earthworms, usually subterranean burrowers, with eyes hidden 

 under scales, with a non-distensible mouth, with teeth restricted 

 either to the upper or to the lower jaw. "The palatine bones 

 meet, or nearly meet, in the base of the skull, and their long axes 

 are transverse ; there is no transverse bone ; the pterygoids are not 



