THE ORDEE OF SNAKES— OP/f7DL4. 



The principal cliaracteristic of this order is an exceedingly elongate body, 

 covered with scales, and either destitute of limbs, or provided with very 

 rudimentary ones, in the form of a spur on each side of the vent. 



Snakes propel themselves by lateral undulations, with the aid of 

 sharp-edged abdominal plates, and loosely articulated ribs moving with the 

 vertebral column, as thus described by Gtinther : — " When a part of their 

 body has found some projection of the ground which affords it some 

 point of support, the ribs, alternately of one and the other side, are 

 drawn more closely together, thereby producing alternate bends of the 

 body on the corresponding side. The hinder portion of the body being 

 drawn after, some part of it finds another support on the rough ground 

 or a projection ; and, the anterior bends being stretched in a straight 

 line, the front part of the body is propelled in consequence. During 

 this peculiar kind of locomotion, the broad shields of the belly are of 

 great advantage, as by means of the free edges of those shields they are 

 enabled to catch the smallest projections on the ground, which may be 

 used as pomts of support. A pair of ribs correspond to each of these 

 ventral shields. The snakes are not able to move over a perfectly smooth 

 surface." 



The number of abdominal plates generally corresponds to the 

 number of vertebrae, the ribs being double that number. These plates 

 are of some value as a distinguishing characteristic between venomous 

 and non-venomous snakes. Thus (speaking of Australian species) snakes 

 with more than 240 abdominal plates, are generally not venomous, as 

 so large a number has never been noticed in any other than the Boa or 

 Python tribe, and some of the Tree Snakes of the genus Dipsas. They 

 have neither breastbone or sternum nor eyelids, and both jaws and the 

 palate are usually toothed ; the mandibles, which are united in front l^y 

 an elastic ligament, are generally very extensible. 



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