448 



MOTION. 



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 

 at a, 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 // ; so that 

 in these two actions of flexion and extension 

 the serpent has advanced through a space equal 

 to a c or b h. The velocity of this mode is 

 great, but will manifestly depend on the num- 

 ber 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 larvee of the Geometra, and might, with 

 equal propriety, bear the same designation. 



The Amphisbsena 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- 

 pending themselves from the brandies 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 

 posture ; such is the movement of the deadly 

 Cobra 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 greater than many bipeds and 

 quadrupeds. Their 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 



and aquatic modes of progression. The carni- 

 vorous Caducibranchiates in an adult state 

 present an almost quadrilateral figure, and as 

 many of the osseous elements of the skeleton 

 (which in fishes are separate) are anchylosed 

 together, they give solidity to the framework, 

 and afford levers and fulcra for muscular action 

 to sustain the shocks necessarily connected with 

 a terrestrial mode of locomotion. In the Frog 

 the anterior extremities are short compared 

 with the posterior; the toes are furnished 

 with a broad web, consisting of an expansion 

 of the integuments, a structure which, witli the 

 length and strength of the posterior extremities, 

 renders them well adapted for leaping and 

 swimming. The eight vertebrae have a ball 

 and socket articulation, which gives them 

 some degree of motion on each other. Their 

 legs being directed horizontally prevent t!ie 

 Amphibia from supporting their trunks above 

 the plane of position. 



In a state of repose, the Frog assumes a 

 sitting posture ; the thighs are flexed forwards 

 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 posterior 

 extremities, leaving the anterior extremities 

 either free or lightly touching the ground. The 

 legs, in a state of flexion, are ready on the 

 least alarm to project the body forward by 

 their sudden extension. 



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 diffi- 

 culty, unless chased at a great distance from 

 the water. It will also spring over a wall five 

 feet in height. The Hy la, or Tree-frog, has each 

 of its toes furnished with a concave disc, which 

 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 Kan a 

 esculents and Ratia pi pa are pal mated for 

 swimming, those of the Kana bufo semi- 

 palmated, and the liana calomella and others 

 have two osseous tubercles on the palms of 

 the hands, which enable them to climb the 

 planes of old walls in order to secrete them- 

 selves in the crevices. 



The urodelous kinds of Caducibranchiates 

 are adapted for land and water ; those adapted 

 for terrestrial progression have the tail of a 

 cylindrical form, as in Salamaudra, whilst, those 

 adapted for the water, as the Triton, have a 

 pisciform tail, the planes of which are directed 

 vertically. 



The perennibrauchiate tribes of Amphibia 

 residing constantly in the water, and with very 

 rudimentary atlantal and sacral extremities, 

 have the trunk elongated and pisciform, and 

 the tail compressed laterally to give a greater 

 impulse in swimming, as in the Proteus, the 

 Axolotl, Siren, &c. 



Saurian Reptiles. The Sauria have com- 

 monly four legs, but a very few are restricted 

 to two. Of these, some are organized for pro- 

 gression on land, others for locomotion both by 



