ilt 



LOCOMOTION OF ANIMALS. 



LOCOMOTION OP ANIMALS. 



5*0 



with UM> length of the step a rightnuigled triangle, o that the height 

 of UM bead of the thigh-bone from tbe ground and the length of the 

 extended i leg being given the length of the step may be found. In 

 Trjr quick running the forward leg, which supports the body, is much 

 bent, and the centre of gravity of the body brought nearer to the 

 ground. ThU U nirnmrj in order to accomplish the greatest Ifiigtli 

 of stop in the leatt portion of time ; the time of each atep is also 



one reaches the ground, so that the bind leg performs a portion of ita 

 are of oncillatiou whilst the body move* through the air unsupported 

 by either leg, and the bird U thus alternately supported by one leg 

 during a abort period and left altogether unsupported by either leg 

 during a longer period, as in man. 



As we find that the ostrich in speed excels the horse, and the 

 cassowary the grayhound, which are reckoned among the swiftest of 

 quadrupeds, we at once perceive that these birds do not require the 

 aid of their wings to raise them in the air in order to escape from 

 their enemies; and if the intelligence of the ostrich were in pro- 

 portion to its speed the mounted Arab would never be able to over- 

 take it in the chase, but as it direct* its flight in a circular instead 

 of a straight course, as in Jig. 40, its pursuer takes advantage of ita 

 ignorance of one of the most simple geometrical facts, namely, that 

 toe nearest path between two distant points is a straight line. Hence 

 it appears that though its safety absolutely depends on the knowledge 

 of toe oourae it should take in flight, it has never solved this important 

 problem; and, notwithstanding its greater bulk of brain, it is far 

 inferior in point of sagacity to the dimunitive bee, and many other 

 insects which display considerable skill in the geometrical construction 

 of their habitations, and are known (by careful observation) to take 

 the shortest road in their flight from one place to another. 



The Lizards and Crocodiles present divers! Bed organs of motion. 

 Amongst the former, the gecko is supplied with a peculiar pneumatic 

 apparatus in the feet by means of which it has the (lower of exhausting 

 the air beneath the toes, and U thus enabled to climb vertically the 

 smooth surfaces of walla, and to walk in an inverted position along 

 the ceilings of rooms. This provision is advantageous to the animal 

 when pursuing the insects on which it preys. In many of the lizards, 

 such aa the chameleon, the tail is in like manner used to secure them 

 more steadily on the branches of trees : the hand is furnished with 

 two thumbs opposite to three fingers, and the foot with three thumbs 

 opposed to two fingers. By this arrangement the animal is endowed 

 with considerable facility in taking hold of the branches, being thus 

 provided, as it were, with four hands. 



straight line, and from this cause may be easily avoided by man 

 should he be pursued by one of these amphibious monsters. 



The Tortoises are slower than the crocodilean reptiles. Like the 

 latter, they cannot twist the body on itself; and the ponderous case 

 within which they are inclosed, and which they drag along witii the 

 body, resists the freedom of motion of the legs at those points where 

 they pass out of the solid case at a and 6 in the following figure (41). 

 This renders their pace exceedingly slow. Their carapace or shield 

 serves however to protect them from injuries arising from the tread 

 of heavy quadrupeds, and is essentially useful to them during their 

 occupation of burrowing. They move on the principles of mamuiife- 

 . rous quadrupeds. 



\ I 





Fig. 41. Amboyna Box-Torloite. 



Serpents. We have seen that the crocodiles and tortoises possess 

 i little or no power to turn their bodies to the right or to the left ; and 

 also that it occupies the last-named animals a long time to change 

 their course from one direction to another. Serpents, on the contrary, 

 have a very great range of lateral motion ; and indeed, destitute as 

 they are of legs, were the bones of the back as iinmoveable as those 

 of the tortoise, they would be deprived of the power of locomotion ; 

 but being endowed with very great mobility of the vertebra;, they 

 are enabled, notwithstanding the wont of legs, to climb trees, to run 

 with considerable speed on the ground, and to swim rapidly in riven 

 and lakes. The scales, which are seen on the belly of the animal, 



/-- ''"&' 









' 



Fig. 42. Hinged Knake. Vertical motion. 



Tbe Crocodile* are furnished with four leg*, and can walk and run 

 oo solid* like mamuiifcrotu quadrupeds. The bones of the neck and 



enable it to lay hold of fixed object* on the ground, and by tho 

 alternate elongation and contraction of the body, it glides along with 







Hg. 43. Ringed *nake. lateral motion. 



are however no locked together that they cannot turn or twist great celerity. There are several ways in which serpents move, but 

 body skUwmys except in an exceedingly limited degree. They the most common arc the vertical and the lateral modes, seen in 

 consequently obliged when moving rapidly to keep in nearly a Jiyi. 42 and 43. 



