OF THE UNITED STATES 



143 



Several years after, Professor Cope, of Philadelphia, found this 

 structure developed in other genera of American snakes, and he 

 published a very important and interesting article upon the sub- 

 ject (Amer. Nat., Feb., 1891, p. 156). Pull snakes are entirely 

 harmless, and at the same time very handsome and most engag- 

 ing reptiles to study. It was in The American Naturalist, too, 

 that I published the first recorded instance of our common Plack 

 snake attacking man. It was a personal instance, and was 

 printed in the April number of that journal for 1891. 



In a former paragraph of this chapter it was stated that in ac- 

 cordance with the opinion of Dr. (Itinther, of the Pritish Mu- 

 seum, that the ribs of snakes were their principal organs of loco- 

 motion. I do not altogether concur in this opinion, but rather 



Fig. 38. Left Lateral View of the Head of a Bull Snake. 



Natural size. Lettering the same. Drawn as in Fig. 37 by the Author. 



incline to the view of Packard as expressed in his Zoology (pp. 

 496, 41)7). This eminent American naturalist there says: "The 

 peculiar gliding motion of snakes is effected by the movements of 

 the large ventral scales, which are successively advanced, the 

 hinder edges of the scales resting on the ground and forming 

 fulcra; resting on these, the body is then drawn or pushed rap- 

 idly forward." It seems to be aow a well-settled fact that snakes 

 never move over the ground by alternate bends of the body's 

 length, the movement being in a vertical plane. On the contrary, 

 they glide over the surface by a wriggling motion in the horizon- 

 tal plane. Then, again, in striking at their enemy or prey, they 

 never entirely quit the ground, or lose contact with it. The part 

 that does that is only about the anterior fourth of the body, 



