40 ON THE PHYSIOGNOMY OF SERPENTS. 



Mliicli is in the centre, is slightly elevated above the other 

 parts ; but having the faculty of bending the body in a 

 thousand different positions, they are often found simply 

 extended on the ground with the body undulated in si- 

 nuous contours. To produce progression, the serpent 

 has merely to unrol his spires ; resting himself afterwards 

 on his tail, rebending his body in successive lateral undu- 

 lations, and, applying to the ground the numerous points 

 of contact which the anterior extremities of the ribs pre- 

 sent, the reptile is pushed forward and transported with a 

 celerity proportional to the efforts or power of the instru- 

 ments of locomotion. We have already remarked on this 

 bead, that the progressive movements of Ophidians are 

 almost all executed in the same manner, and that the tail 

 but aids the locomotion differently, according to the mo- 

 dification which its form undergoes in the different tribes. 

 Very often, in order to observe what passes around them, 

 serpents raise themselves perpendicularly, supporting 

 themselves solely on tlie tail, or on a part of the abdo- 

 men ; their trunk is then rigid, and perfectly straight ; 

 and most frequently the head is then bent and directed 

 forwards : at other times they bend their bodies as an S, 

 inflating their necks in this position. Suspended perpen- 

 dicularlv from the branch of a tree, the Boa resembles a 

 Stiff body without life. In descending from a tree or other 

 tall object, serpents let themselves simply fall to the 

 gi'ound, — their form, and the elasticity of their parts, pre- 

 venting any dangerous consequences from this fall ; on 

 attaining the gi'ound, the shock they sustain, instead of 

 proving hurtful, impels them forward, and serves as a 

 stimulus to their subsequent movements. 



Serpents have been repeatedly described, that can per- 

 form perfectly a retrograde movement. This peculiarity 

 has been especially attributed to those burrowing snakes 

 that have cylindric bodies, terminated by a tail very thick 

 and obtuse at the extremity ; but as this has neither been 

 certified by well-informed travellers, nor by professed na- 

 turalists, there is room for doubt on this point ; perhaps 

 it owes its origin to the prejudices* of the ancients, who 



* Plin. VIII. 35. ^LiAN, IX. 23. 



