168 



" Superimposition of twists " (§ 71) ; i. e., spring by 

 two rear and two front appuis. 



§ 151. The Double-action Trot or Square-Jump 

 must differ very considerably from the single ac- 

 tion in the movement of the feet, since one fore- 

 foot can no longer be thrown forward by the neck 

 movement, A a^ a'^ (§ 143), while the other fore- 

 foot acts in appui ; on the contrary, the fore-feet 

 when thrown forward must depend for support on 

 the hind feet, or on an impetus derived from the 

 spring of the hind feet. And, also, since all the legs 

 must be affected, before the spring, hy both the body 

 and neck gatherings. 



§ 152. We shall be obhged to add to the sym- 

 bols, § 141, a character representing the right an- 

 terior and left posterior winding lines which can no 

 longer be regarded as alternate, by giving an Italic 

 letter to these last, thus A a* a'*, A', and so on, 

 for the right anterior Hues, B b'^ b^ B', for the 

 left posterior. 



§ 153. In the double trot the anterior winding 

 lines, left and right, acting together throughout 

 their secondary and primary sections, in the ophid- 

 ian S, throw, by change of centres of gravity, the 

 weight on the outer bearings of both hind and both 



