SNAKES. 17 



ground over which they move, yet all the varieties of their locomo- 

 tion are founded on the following simple process. When a part 

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

 it a 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 if 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 loco- 

 motion, the numerous 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 points of support. Snakes are not able to move 

 over a perfectly smooth surface. 



Non-venomous Snakes have generally two rows of short, thin 



Fig. 13. 



Skull of Snake (Python). 

 m, maxillary ; pm, premaxillary ; q, quadrate bone. 



teeth, pointed like a needle, on each side of the upper jaw, and 

 one in the lower; sometimes one or two of the anterior teeth are 

 longer than the rest, but they are not grooved or perforated, nor 

 do they communicate with a poison-gland. Other species have 

 one or more of the hindermost maxillary teeth enlarged, and 

 provided with a longitudinal groove. The Snakes with such 

 long grooved posterior teeth are provided with a small poison- 

 gland and possess slight poisonous properties, paralyzing their 



