130 FORM AND ACTION. 



impulse. No sooner is the centre of gravity of the body disturbed 

 by the displacement of one of its supporters, than an effort is made 

 to rectify the derangement; the rectification, however, is hardly 

 accomplished before another act of disturbance is commenced : thus, 

 by repeated acts of projecture in the fore limbs, and as repeated 

 acts of propulsion in the hind, is the animal machine moved for- 

 wards at rates correspondent with the impetus generated by these 

 movements. 



When once set in motion, like the wheels of a carriage, the 

 limbs instinctively continue in similar action or pace until some 

 fresh mandate is received by them from the sensorium, that be- 

 coming the signal for some change in the action or pace. The rate 

 the animal is moving at is either augmented or diminished, or his 

 movements are altogether arrested, at his own will and pleasure. 

 And though his master, as his rider or driver, may assume the 

 control over them during the animal's working hours, yet could 

 neither rider nor driver effect any thing without the assent of the 

 animal himself; and it is ever a great deal best to obtain this 

 assent through kind and conciliatory treatment than to extort it 

 through ill usage. 



Plain and evident as the movements of the quadruped may 

 appear to the common observer, passing as they do every day 

 under his immediate observation, yet have they furnished a theme 

 for difference of opinion, not less in former days than in our own. 

 Borelli, who commences his chapter De Incessu Quadrupedum 

 with the remarkable words, " Egregie in hac parte allucinantur, 

 nedum vulgares homines, sed etiam prseclari philosophi et anato- 

 mici; qui potius falsa? opinioni per manus traditse, quam pro- 

 priis oculis fldem praestare volunt," is the first to fall into error. 

 The movements of the biped are simple and self-evident ; they 

 consist of the alternate advance of the legs, and of the reciprocal 

 shifting of the centre of gravity from one to the other : here there 

 can be no dispute about priority or order of movement. When 

 we have four in place of two legs, however, the case becomes ma- 

 terially altered. It is an easy matter to watch two legs ; but it is 

 difficult, nay, in quick movements impossible, to keep the eyes 

 so fixed upon the motions of four as to say in what order of suc- 

 cession they are actually moving or treading the ground. In order, 



