448 
by the flexion and elevation of the trunk in a 
single arc or curve, as seen in fig. 243. If 
during the extension of the reptile the tail be 
ata, it is by flexion advanced to e, during 
which motion the head is fixed at 6; the tail 
being then fixed at e, the body is suddenly ex- 
tended, and the head projected to h; so that 
in these two actions of flexion and extension 
the serpent has advanced through a space equal 
toaeorbh. The velocity of this mode is 
Great, but will manifestly depend on the num- 
r and magnitude of steps taken in a given 
time. This mode of progression is that used by 
the rattlesnake, when the greatest speed is ne- 
cessary in pursuit of prey, for instance, or 
in escaping from an enemy. When these 
flexions and extensions are performed with the 
greatest rapidity, the speed of the rattlesnake 
exceeds that of man. The principle of loco- 
motion in the fifth order is similar to that 
of the larve of the Geometre, and might, with 
equal propriety, bear the same designation 
The Amphisbena walks with equal facility 
either backwards or forwards; the lower jaw 
being supported by the tympanic bone, which 
is articulated to the cranium, is used by these 
serpents as a fulcrum for retrograde ;progres- 
sion. The Boa and the Python climb trees with 
great facility ; this they effect in a spiral curve, 
the scuta of various segments, through their 
enormous length, laying hold of the bark ; and 
aided by the great flexibility of their vertebral 
column, they are enabled to ascend in opposi- 
tion to the force of gravity. They select trees 
in the vicinity of streams and rivers, and sus- 
ending themselves from the branches in an 
inverted position by means of their prehensile 
tail (which is furnished with a corneous hook 
on each side the anus), seize and crush qua- 
drupeds even of large size as they approach to 
drink. 
Serpents are also capable of darting, either 
from the curved position or the spiral coil, by 
the sudden elevation of the body to an erect 
sture; such is the movement of the deadly 
obra de Capello in its attack on the uncon- 
scious traveller, and in the same manner the 
common Viper inflicts its less dangerous wound. 
The erection of the trunk, either from the ver- 
tical curve of the Rattlesnake or the horizontal 
coil of the Cobra, is said to generate a projec- 
tile force sufficient to raise the reptile above 
the plane of motion. Although destitute of 
the limbs with which the higher vertebrata are 
furnished, serpents are endowed with the power 
of transporting themselves from place to place 
with a velocity ter than many bipeds and 
uadrupeds. eir locomotive powers enable 
them to chase and capture their prey ; to stride 
across plains; to ascend and descend hills and 
precipices, inaccessible to most of the higher 
animals; to climb trees; to swim lakes, rivers, 
and seas; and thus not only to provide the 
means of subsistence, but also to choose those 
places of abode which are most suitable to their 
wants, pleasures, or habits. 
Amphibia —In consequence of the amphi- 
bious nature of many Batrachia their loco- 
motive organs are adapted both to terrestrial 
MOTION. 
and aquatic modes of progression. The earni~— 
vorous Caducibranchiates-in an adult state 
present an almost quadrilateral figure, and as_ 
many of the osseous elements’of the skele 
(which in fishes are separate) are anchy 
together, they give solidity to the framework 
and afford levers and fulera for muscular action 
to sustain the shocks necessarily connected with 
a terrestrial mode of locomotion. In the Frog 
the anterior extremities are short compa 
with the posterior; the toes are 
with a broad web, consisting of an expansio 
of the integuments, a structure which, with the — 
length and strength of the posterior extremities, 
renders them well adapted for leaping and — 
swimming. The eight vertebre have a ball 
and socket articulation, which gives them 
some degree of motion on each other. Their 
legs being directed horizontally prevent the — 
Amphibia from supporting their trunks above 
the plane of position. ws 
In a state of repose, the Frog assumes a 
sitting posture ; the thighs are flexed fo 
and outwards ; the legs are flexed backwards 
on the thighs; the lengthened feet and toes are 
again directed forwards; the trunk is inclined 
to the vertical plane at an angle of about 
45°, which brings the centre of gravity within 
the base formed by the pelvis and posteri 
extremities, leaving the anterior extremities 
either free or lightly touching the ground. 2 
legs, in a state of flexion, are ready on the 
least alarm to project the body forward by 
their sudden extension. 1 
’ Lill 
rae 
. 
The Bull-frog is said to project itself six or 
eight feet at each leap, and the leaps are re- 
peated so rapidly that it is captured with ¢ 
culty, unless chased at a great distance from 
the water. It will also spring over a wall five 
feet in height. The Hyla, or Tree-frog, has eae 
of its toes furnished with a concave disc, 
acts as a sucker to enable the animal to attach 
itself to branches of trees, amongst which it 
runs with great facility. The feet of the Rana 
esculenta and Rana pipa are palmated for 
swimming, those of the Rana bufo semi- 
Imated, and the Rana calomella and oth 
ave two osseous tubercles on the palms o 
the hands, which enable them to climb th 
planes of old walls in order to secrete them: 
selves in the crevices. ¥ 
The urodelous kinds of Caducibre 
are adapted for land and water; those adapte 
for terrestrial progression have the tail of 
cylindrical form, as in Salamandra, whilst tho 
adapted for the water, as the Triton, have 
pisciform tail, the planes of which are direc 
vertically. ss 
The perennibranchiate tribes of Amphib 
residing constantly in the water, and with 
rudimentary atlantal and sacral extremitit 
have the trunk elongated and pisciform, a 
the tail compressed laterally to give a greate 
impulse in swimming, as in the Proteus, th 
Axolotl, Siren, &e. = 
Saurian Reptiles.—The Sauria have co 
monly four legs, but a very few are restr 
to two. Of these, some are organized for 
gression on land, others for locomotion both 
os. 
Ci det) 
