SNAKES OR SERPENTS 709 



Many Ophidians become lethargic during extremes of temperature, 

 or after a heavy meal. 



Snakes are especially abundant in the Tropics, but 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. 



True Ophidians first occur in Tertiary strata. 



Some Examples of Ophidia 



Typhlopidae. 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 connected with the quadrates." The quadrate articulates 

 with the pro-otic, for there is no squamosal. 

 Example. — Typhlops, very widely distributed. 

 In other Ophidians the palatines are widely separated, and their 

 long axes are longitudinal ; transverse bones connect palatines or 

 pterygoids with maxillae ; the pterygoids are connected with the 

 quadrates. 

 In innocuous snakes the poison gland is not developed as such ; the 

 maxillary teeth are not grooved. 



Examples. — The British smooth snake {Coronella IcBvis) ; the 



British grass-snake {Tropidonotus natrix) ; the Pythons ; the 



Boas, of which the Anaconda {Boa murina) (30 feet) is the 



largest living Ophidian. 



In venomous snakes some of the maxillary teeth are grooved, and in 



the most venomous the groove becomes a canal open at both ends. 



Examples. — Cobras, Naja tripudians (Indian), Naja haje 



(African) ; the Hamadryad {Ophiophagus elaps), eating other 



snakes ; Coral-snakes {Elaps, etc.) ; Sea-snakes {Hydrophis, 



etc.), with paddle-shaped tails. The British adder {Pelias 



berus) ; the rattlesnake {Crotalus), with a rattle formed 



chiefly from epidermic remnants of successive sloughings ; 



the African Puff-adder {Clotho arietans). 



Fifth Order : Crocodilia. Crocodiles, Alligators, Gavials 



General Characters. — The Crocodilians are carnivorous 

 fresh-water reptiles of large size, now represented by a few 

 genera, e.g. Crocodilus, Alligator, and Gavialis, 



