M. Dumeril on the General Movements of Serpents. 241 
When a serpent requires to raise itself, or place a portion of its body 
in an upright position, if it then meet with a solid object, it applies its 
trunk to it, elevates and stiffens its body by directing its efforts to the 
fixed point, and making the series of plates in the anterior part of the 
belly, and consequently those succeeding, form an arch. When, on the 
contrary, the ground is level, the same movements are produced on the 
parts of the trunk which rest on the ground. The whole anterior region 
of the body there finds a kind of solid fold, which supports it like the 
base of a pillar raised upon itself. The serpent is then seen to carry its 
head vertically, somewhat like a swan’s neck, in order to turn and move 
it gently in every direction, as may be witnessed in the Najas or hooded 
snakes, when they assume various singular attitudes, appearing at tlie 
same time to follow the measure of music varied by the instruments or 
songs of the Indian jugglers, who often publicly exhibit these kinds of 
dances, in which the snakes have been previously exercised by various 
manceuvres. 
The active leap is produced, as is known, by the darting of the whole 
living mass, which all at once completely and voluntarily leaves the sur- 
face on which it rested, in order to spring freely over a distance more or 
less considerable. Although destitute of articulated limbs, serpents still 
enjoy this power, but by processes as peculiar as can well be conceived. 
Thus at times the reptile, having its body rolled in a circle on itself, 
keeps it stretched like an elastic spring, remaining spirally twisted by 
the contractile force of the muscles of the internal lateral region, concave 
or concentric to the spine ; but all of a sudden it relaxes itself by the 
instantaneous shortening of the convex or external edge of the cireum- 
ference, which, becoming suddenly elongated or extended, unfolds with 
great force and rapidity. Sometimes, in order to effect a more rapid 
change of place, to recede or advance with more celerity, the serpent 
executes in this way a series of successive bounds, which are produced 
in the direction of its length by means of undulations on the sides, from 
before or from above downwards, and reciprocally, with slight sinuosities 
which alternately correct each other. 
The act of swimming, whether it take place on the surface or under 
water, is likewise produced by these diverse undulations. It is a mode 
of progression similar to that which takes place on the earth or on move- 
able sand. In these circumstances the serpent, being able at pleasure to 
become heavier or lighter than the water it displaces, in consequence of 
the variable quantity or volume of gas contained in its very long lungs, 
can support itself on the fluid, and communicate to it an impulsive power. 
It avails itself of the reaction produced by the shock it gives to the am- 
bient fluid, It is principally by the tail and the hinder part of the trunk 
that the serpent supports itself in water. For this purpose the tail is 
often widened and strongly compressed from right to left, in the form of 
a vertical fin, as may be seen in the Hydrophides, Enhydres, and Pla- 
