240 M. Dumeril on the General Movements of Serpents, 
tical position, at least in part, by stiffening certain regions of their spine 
which they support and cause to moye on another portion of their own 
body. Some of them remain immoveuable, and in ambush, on trees, hav- 
ing their long folds interlaced among the branches to which they cling, 
suspending and balancing their mass in order to dart suddenly to a great 
distance, as if by the movement of a sling. Others burrow in the earth 
or insinuate themselves into subterranean galleries, either for the purpose 
of shelter, or to prey upon the animals which live in them. There are 
some which swim and support themselves on the surface of the water, or 
plunge into its depths ; for it is there only that they can find and pursue 
their victims, which they must seize alive and swallow at a single mouth- 
ful, or at once, without dividing it. 
Creeping is the most general mode of progression among’ serpents ; 
this act is produced by a series of successive contractions communicated 
to their long spine by the numerous muscles inserted in the vertebree and 
ribs. In order to understand rightly how this act, or reptation, takes 
place, we must suppose that the animal, being stationary, or having made 
a momentary pause, has halted on a surface more or less resisting, on 
which it finds a point of support. Most commonly it is the belly or un- 
der part of the body which is applied to such support. It first raises the 
posterior moveable edge of one or more solid horny plates, with which 
the abdomen and tail are furnished, in such a way as to move forward 
the plates situated further forward, on which it then seems to glide, then 
successively on all those which precede ; for these plates act by means 
of the ribs which are inserted into them, so that they move like so many 
feet, which would nearly correspond to those we observe in the body of 
Juli and other myriapodous insects. These movements taking place at 
the same time, and in the same manner, follow each other regularly, and 
are repeated in a beautiful successive order along the whole length of the 
inferior region of the body. We may thus conceive how the direct dis- 
placement of the mass is produced, as it is necessarily urged from behind 
forward, so that the head is carried more and more in advance, and the 
tail follows nearly in the same direction. ‘This progression, however, in 
the greater number of cases, takes effect at the same time on the lateral 
parts of the body by a series of undulations or sinuosities, which obtain 
for the serpent points of support on the objects which present some re- 
sistance to it on the right or left. It may then be observed to curve its 
spine regularly according to its length, to produce sinuous and arched 
lines in it, which are successively effaced, become formed anew, and re- 
produced as often as the obstacle encountered continues to offer resist- 
ance to the pressure. This is the mode of moving we observe in eels, as 
well as in:certain saurians with a very long body and destitute of feet, 
such as the species of the genus Anguis; and it is therefore likewise 
called, when it takes place among these animals, a serpentine motion, 
Such is the mechanism of creeping or reptation, 
