M. Dumeril on the General Movements of Serpents. 239 
reality the greatest number of vertebree of all animals, as frogs and other 
tail-less Batracians have the smallest, only eight or nine at the most. 
It is remarked, moreover, that the vertebral bones are comparatively 
longer and narrower in the climbing species which live habitually on 
trees. 
It is owing to the prodigious number of bones composing the vertebral 
column, and their great mobility, that the body of serpents owes its ex- 
treme flexibility, and the power it possesses of adapting itself to all sur- 
faces, whatsoever may be their curvatures, in order to find points of sup- 
port. Their movements take place principally to the sides, from the 
right to the left, and reciprocally ; sometimes, but more rarely, from 
above downwards, and from before backwards. Although each of the 
pieces of the spine should turn very little on its axis, the smallest de- 
viation which can take place, becomes the centre of a flexible ray repre- 
sented by the prolonged part of the column from the side of the head, or 
towards that of the tail. As progression most frequently takes place by 
lateral movements, it is to that direction that the reciprocal gliding upon 
each other of the vertebral articulations seems best adapted. 
The ribs of serpents are prolonged levers, lateral appendages of the 
vertebra, which, although destined for the mechanical act of respiration, 
serve still more for progression. As they are not joined together by a 
sternum, they can recede from each other sideways, and from before 
backwards, in the different parts of the extent of the trunk. Their num- 
ber is considerable ; it amounts nearly to three hundred and upwards in 
some Pythons and Trigonocephali. Half that number is found in the 
viper, so that no kind of animal has in reality a greater number of ribs 
than the ophidians. 
We shall not examine in this place the numerous fascicles of muscles 
which, fixed to the different parts of the vertebrae and ribs, produce uni- 
formly, and repeat on each of these bones the partial movements from 
which the acts of locomotion arise ; the latter are to be examined ina 
collective sense. 
Sometimes it is the weakness of a supple body, slender and very flexible 
throughout its whole length, that permits or facilitates agility and nimble- 
ness in the locomotive power; sometimes, on the contrary, it is the 
strength and rigidity of the trunk which, joined to its considerable volume, 
and the energetic and successive action of the muscles, determine the 
prodigious power which very large serpents can exert when they envelope; 
strangle, and crush in their tortuous folds the bodies of the animals de- 
stined to become their victims. 
When serpents creep, they change their place by alternate flexuose 
undulations or sinuosities. They then draw themselves in, and again 
turn outwards, and fold their body upon itself, forming so many curves 
in the form of the letter S, by numerous contours and varied revolutions ; 
but they can likewise stand erect and raise themselves into a nearly ver- 
